Jump to content
Sign in to follow this  

FAQ-master link thread.

Recommended Posts


Before we start I want to ask the following, please ignore the peer pressure and do not;

Remove the slide from the carb or

On the new generation of engines remove the hydraulic cam chain tensioner, (without good reason)

Buy an aftermarket fuel screw made from aluminum even with a catchy name, or

Buy an aftermarket cover for your accelerator pump.

Remove the spark plug cap by trying to grip it and allowing your hand to slide up the cap so your actually pulling on the wire. When you do have that cap off lube it with dialectric silicone, AKA “tune up grease” available from an auto parts store.

In each case the opportunity to do more damage then good is greater then the potential good.

Also one definition, when I say XC or XC line I am referencing EXC/MXC/XC. When I say SX line I am referencing SX & SMR.

Side Stand: This piece was designed to hold the bike up, period, its light, racy and thus not bullet proof. Don’t even think about sitting on the bike or kick starting it on the stand!

Don’t trust the factory on air filter oil! Do it yourself, grease the seal.

Loctite the shift and kick lever bolts as well as the rear chain guide where it bolts to the swing arm. Some recommend getting a bolt one size longer for the shift lever making better use of the threads in the bottom of the hole.

Block the bike up on a work stand, remove the rear wheel. Slide the brake caliper mount forward and off of the peg on the swing arm, behind it there is one of 3 big plastic plugs, the others are left inside and front center. Those plugs need to be popped out, sealed with silicone and re-installed. Next remove the chain adjuster bolts, take them out if stiff go buy a tap and chase the threads now while you can, then get as much antisieze compound in the adjuster threads hole as you can, reinstall the bolts and wheel. Remove the rear shock, very easy, the bike is already blocked up so the wheel drops, remove the shock bolts and it will slide down & back, then block the wheel up until the swing arm is mid travel, find that point where the arm points in a straight line with the front sprocket, and adjust the chain in this location, it will seam too loose when extended but when you put the shock back on make good notes of its slack, never set it tighter than this!! When your riding buddies say your chain is too loose, ignore them!

Crankcase ventilation: The per pressure to modify the vent hose parallels teens & smoking. Please bear with me for a minute. On a single cylinder engine when the piston goes down the crankcase volume goes down by the engines swept volume (such as 450cc). Piston goes up it reverses. The system that vent the crankcase is complex. KTM had a pretty good idea of what they where doing when they routed the hose to the carb inlet on the XC line. I question their thinking on the SX where they run the vent hose out the back. Example, if your crossing a stream in deep water at low idle, do you want dirty water going into the engine when the piston goes up? My way is leave it alone on the XC line, if I had an SX it would either be into the carb bell like an XC or up into the steering head, a design that I see as acceptable but no reason to change to from the XC routing. The SX system I don’t find acceptable.

While we are on the subject of hoses and stream crossing read Carb Setup 101 and make the mod described there on the carbs hoses, the design that Kehein provides was engineered for fire safety which is all very nice but leaves you dead in the water in stream crossings.

Coolant Level: First on the right side of the head (RFS engine) near the spark plug is a 8mm hex screw. Unscrewing this bleeds out any air in the head, it should ozze a bit of coolant, re-install, next on the right radiator is another identical screw, we should do the same except we need to lean the bike to the left like it was on the side stand! When done the coolant level needs to be checked at the left radiator must be no higher than ¼” in that tank, bike upright! If it is higher as the engine comes up to temp it will burp excess coolant out onto the head pipe and you will be all panicked that your bike is overheated when it may not even be up to normal temp yet.

Oil should be checked at the right side site glass, must wait quite a while after the bike was run to allow for drainback, bike must be upright/flat/level and the oil should be between just visible and ½ way up! If overfull expect the bike to smoke and be sluggish and blow out gaskets.

Always check tire pressures, my preference is around 13lbs, the lower you run the more you are prone to flat tires and damaged wheels and the faster you are the more air you need.

I like having a stem nut and metal valve cap! If you have the nut & washer on there and against the rim the first you know the tire is slipping on the rim is when you have a flat from the stem being torn out of the tube. Not good!

If you leave the nut off you will see the stem angle change and hopefully have opportunity & foresight to correct it before it rips the stem out! However if your tire is very low and you try to inflate you run the risk of losing the stem inside the wheel! Also not good!

My way; Stop by an auto parts store and buy a few of the metal valve caps. Uscrew the stem nut so it is snug against the metal cap and you have the best of both worlds. Stem will tilt rather then rip the tube, the nut will keep the stem in place when you are putting air in.

Idle speed the engine needs to idle just a bit faster than common, 1,850 being the right number. A lower setting can leave the “automatic de-compressor” still activated and this will kill low end power to the point of causing a “hiccup”. Its probably just right as delivered and you probably feel you should turn it down?

Break in: Many theories out there on how to best break in an engine but First and Foremost DO NOT take a new bike immediately onto a trail where your going to get grid locked, crawling along at zero MPH and or pushing up a hill, the new engine is going to make a lot of heat as it breaks in so go someplace where you can maintain some momentum and keep a good flow of air thru the radiator! General routine run it 3 hours, change oil and adjust the valves.

For valve adjustment, please read one of the two separate articles (SXF and RFS) here devoted to that subject.

Also at about 3 hours you need to change your oil! New filters are recommended, there are many prices & sources, I see no reason to change them every time after this initial service as there is a pair of pick up screens that catch most of the debris. There are three “drains” that we are going to deal with at least for this first service!

A: Drain plug, the actual drain is in the left rear corner, 13mm hex and has a copper washer that we do not want to loose, while it is out the magnet should be whipped clean of metal. Note the process of breaking in new gears causes them to shed some slivers that will be stuck to the magnet.

B: Side screen, take a socket that fits the outer edge (bigger then the 13mm that fits the hex) and give it a whack with a steel hammer, then unscrew the 13mm hex.

C: Bottom screen, this one requires attention as many have problems so get the right tools! Take them with you, when you get back from riding, when the bike is warm!!! Lay it on its side, on the bottom of the engine inboard from the toe end of the shifter is an 8mm Allen plug that is aimed up at a strange angle and it is tighter than one can comprehend! Put about a 13mm socket over it and give it a firm whack with a metal hammer, no mallets. Then we need a good 8mm Allen socket, an extension bar and a flex bar at least a foot long! Make sure it is in all the way, not blocked with mud. Now I want to pause and try to explain what good mechanics know about turning wrenches! There are two ways:

Novices way; Lets say the handle portion 2 inches out from the part engaging the fastener. If you just pull on the wrench handle two things happen, A) there is a force trying to turn the fastener, and, :ride: there is a force trying to tip the wrench caused by that 2 inch offset! This tipping tips the fastener thus making it bind in the hole.

Experienced mechanics way: Use a socket, an extension and flex bar and while pulling the wrench left with one hand the other is applying equal and opposite pressure to the top of the extension with the other. This way there is no tipping action to bind the threads applied to the fastener and it will come out. If your making a post wineing that you stripped out the hex because it was built lighter then a Caterpiller tractor I think you made some shortcuts! It is a race bike and light weight comes before trash proof.

Upon removing it note the brass washer, once removed the bike should be stood up so oil can drain, screens cleaned. When re-installing the threads should be lubed, anti-seize compound if you have it, then not real tight, spec is 7 ft lbs?

When re-installing this screen/plug take a long Phillips screw driver (not a replaceable tip type, or long skinny punch and slide it into the hole so you can note and replicate the odd angle, then following that angle slide the screen and plug in, be careful that you have it at that same angle and start the threads with care. I don’t wana hear that you cross threaded that piece!

At the same time we need to change the filters, on the RFS there are two, located below the carburetor. When ready to reinstall the bike should be leaned over again so the filters cavity can be substantially full of oil.

SXF Footnote, These engines have a much larger oil pump and when started cold the oil hits the filter hard and they have been known to collapse! To help the filter survive first fill the filter cavity, use only 10/40 in the winter and avoid revving the engine when the oil is cold!

Refill with about one qt of high grade synthetic, 10/40, is engine uses so little oil that the oil is hot and you do not want anything but synthetic! I use Golden Spectro, others Belray, Lucas, Motul, etc, top quality stuff only!!

Start the engine, allow it to run for a bit so the oil is circulated thru filters etc, then leave the bike sitting upright such as on a work stand and let it sit no less then a couple hours, overnight would be preferred, then check the oil level at the site glass. We want the oil level no higher then the middle of the glass! Note higher oil level will block the hole where the crankcase vents. This will lead to excess crankcase pressure and can blow out gaskets.

Carburetion: This subject is so complex I have broken it into two separate articles, Carburetor 101 and Accelerator Pump 101.

Bike washing & modern four strokes. Years ago when I worked on a lot of two strokes one observation I made was I was repairing more rust damage then wear/use. Common issue was rod bearings. The hard steel of the crank pin & roller bearings gets the rust, main bearings not much better. (Don’t get me started on what I think of 40 or 50 to 1 premix). Since those days I have always advocated, “after you wash your bike you need to start it and run it for a bit”, until the muffler is warm may be a reasonable guide. The four strokes issues are different but similar. Since KTM went to Ti valves in 03 on the 450SX their otherwise excellent Bronze valve guides have been a high wear item. Then with the SXF and all 06 4 strokes they switched to Sintered Iron guides. Husky switched to these in 04, even Porsche went to them at some point, they are excellent and I am using them as a replacement in the earlier models now. Being a Husky rider I follow them on another chat room and recently something came up that is bound to happen here as well so I thought I would post this as a post wash reminder. What has happened to a couple guys and a very respected tech said he had been seeing it on other color 4 strokes as well. Guy washes his bike and parks it, weeks later pulls it out and it had zero compression. Drags it to the dealer, they pull the head pipe and find the iron guides all rusty! The fix is squirt penetrating oil on the guides/stems, then rock the crank forward and backward so the piston bumps the valve shut to what degree it will until it frees up. Prevention is run the bike after that wash. This applies to any bike but those with 06 & newer KTM 4 strokes may not get away with the level of lack of care that the older bikes got away with. Personally, I don’t see this type of thing as a “problem”, just run the engine!!

Fuel cap engineering has not been KTM’s strong point, there are a couple issues, first is leaking, sorry I have stared at the cap seal of the 07’s and I don’t’ see an answer, the other is venting. Any tank has to be vented to allow air IN to replace gas as it flows out. You have seen or owned one of those vent hose check valves that most shops sell. They work nice in most applications, go down a ultra steep hill and gas does not drool out. The KTM RFS engine creates another problem! The engine is bigger then most dirt bikes and in the interest of keeping weight low the tank surrounds the tank so the engines heat goes to the gas!

Now the gas is expanding in the tank faster then the engine is burning it off. There are two test we need to run;

A: Does air flow in, B: Does air flow out?

The air out is easy, remove the gas host from the carb, pivot it up so its above fuel level, whip it dry, take a deep breath and blow on it while turning the petcock on. Air should bubble up thru the gas and vent out thru the cap. If the cap is not venting it will build pressure in the tank and you will be blowing against a solid vessel.

Air in is not much harder, take the same fuel hose and route it to a fuel can, turn on the fuel and let it flow. If the tank is not venting in after a bit the flow will decrease, so after a couple minutes while watching the flow, just remove the cap. If the flow increases we have a vent problem. Some caps have had a black plastic ball in them that should be removed.

Your EXC is designed for the Mud slopper Enduro use and as such has a chain guard to keep mud that comes around with the tire from dumping on the chain. To my thinking that is the most misunderstood piece on these bikes, designed for a use and often tossed, wana look like a motocross guy at any expense, toss it, wanta get some miles out of your chain & sprockets, maintain it, when it gets trashed its probably the least expensive piece on the bike.

Deceleration popping is addressed in a separate article.

SXF, very important, when you start the engine, do not rev it! Some combo of Hi oil flow, thick cold oil and hi RPM is you start it then rev it has caused some filters to be crushed by that first wall of oil. Let it warn up for maybe a minute before trying to ride off and at your first opportunity buy a Scotts oil filter.

Also the SXF is sensitive to the volume of gas the AC pump squirts. In 07 they added a “Leak Jet” to the float bowl, on the 05-06 models I would contact JDjetting.com and get their float bowl that uses a “leak jet”, follow his advice on the size, but a #60 would not be an unreasonable spot to start.

07 EXC’s

To get these bikes “street legal” they had to make a couple mods, please do not ask your dealer to make these for you! The fines for a Dealer messing with pollution control are along the lines of “out of business” I would rather you encourage the dealer to not go there. There are two basic mods;

1: MUFFLER: Just inside the back piece you should see a tube with a washer welded to it, just saw off the washer and you have approx what the off road models have.

2: CARBON CANISTER: This is a black box below the front of the swing arm that has vent hoses running to it. What is does is filter gas fumes from the tank or carb thru a block of carbon (visualize a pores bricket). This works fine as long as you do not fill the gas tank, do not lean the bike to either side or ride thru bumps. If your going to do any such activities gas is going to get into those hoses, the carbon is going to get saturated and no longer vent, it can cause fuel starvation as air can not get into the tank to replace fuel as its burned off, can cause some serious nightmares!

I might add that JD has a different jet kit for those that retain this piece, for me, it would be outa here and I would buy the generic jet kit.

The rest of the EXC tune up should be equal to the off road models so the frustrations are pretty minor related to what KTM accomplished!

Other stuff;

Most riders consider it mandatory to have (and I would prioritize in this order)

Hand Guards: A simple fall without them can take out a master cylinder, the best come from Fastway.com.

Skid Plate, can save a ton of problems

radiator guards, if your crash prone

Clutch slave cylinder guard?

Extended fuel screws, there are many brands on the market, hold out for a brass one!

About the author

Dave Hopkins is a former Husky dealer, former off road competitor and mechanic, today sells Real Estate in the Seattle area and as a hobby business does head work on MC cylinder head primarily KTM & Husky. Can be reached at davehopkins@windermere.com

  • Like 3

Share this post

Link to post
Share on other sites


For Keihin FCR carb

Note: do to the complexity of the accelerator pump I have broken this into two sections, the other being Accelerator Pump Set Up 101

Theory: The function of the carb is a controlled siphon! Air is drawn in by the engine, some of it passes thru one of those “air jets” at the air filter end, then passes the orifices above the jets and it siphons gas up thru those jets. Different jets control different functions, “starting” effects the effectiveness of the choke (really an enrichener), “pilot” effects primarily idle, the rest passes thru the “main jet” however it function is blocked by the “jet needle” until the throttle is lifted all the way up, thus the main effects primarily full throttle. The float level effect how much the siphoning has to lift the fuel.

Different models: The first of these that I worked on was a 98 Yamaha. Those had a steel rod for the accelerator pump. These are very prone to the rod rusting and becoming seized in the bronze guide it slide in and the accelerator pump will not work. All of the KTM’s I have met had an aluminum rod.

00-02 KTM’s 400-520 used a 39mm carb (02-250 had a 34), the accelerator pump rod was exposed to the elements on the right side of the carb body had a rubber boot as it passed from the elements to inside. The boot would fail and water & dirt would get inside, the pump diaphragm would fail.

03-05 KTM’s, The accelerator pump got both a screw that adjusts when the pump starts, a black plastic cover to keep the pump linkage clean and the 250 went to 37mm, 450 & 525SX (SMR what ever year it started) increased to 41mm. The have a tab on the side that is commonly used for the BK Mod (see Accelerator pump 101).

06 KTM’s, That tab for the BK mod disappeared and the rear air horn changed.

Throttle travel: US models should not have it but Euro and others models are likely to have a throttle stop. The is screwed into the top of the throttle slide and sticks up from the slide maybe ¾ inch to stop it from opening all the way. It should be tossed either immediately or after a brief break in period.

Throttle Slide: Avoid pulling this out! On the front/engine side of the slide there is a black plate called the “vacuum release plate”. It has a hole about ¼” near the bottom. This plate can be installed backwards which leaves that hole at the top and not visible. When installed wrong the slide drops normal when the engine is off but when running the slide pauses before it complete closing, bike refuses to idle properly and well it just runs ugly.

Throttle Cable: On throttle cable they come with one for you, to open the throttle and one for the Lawyers and Department of Transportation (DOT) to close it. Personally I like to ride with minimal slack in the cable. When you do this on the Kehein it becomes less easy to twist as the pulley on the carb that the cable runs around is a two pieces of stamped steel design which leaves the base of the pulley with a kind of crotch, the cable gets jammed into the crotch and becomes more difficult to operate.

Dave’s way: Don’t let me talk you into something you don’t want to do but I toss the closing cable, the throttle will work so much easier you will never want a closing cable again. As it will work as a spare opening cable you can save it as a spare or for the long distance rider, leave it in place just disconnect both ends.

Fuel Tank Vent: This hose has a couple underrated functions, the one we commonly think of, as fuel is consumed, the level goes down and air must flow in to replace it. What we may forget is these four strokes have the engine and tank so closely integrated that the tank/gas get hot! This is OK but often the gas expands faster than the engine burns it so early into a ride it is not uncommon that if the tank can not vent out the gas becomes under pressure, this sinks the float, floods the engine and frustrates the rider to no end. Tank & cap must be vented to atmosphere both ways.

Dave’s way: Take your gas cap apart and toss the check ball! None in the hose! And while we are looking at that, take a look at where the hose goes? When that gas expands we do not want overflow dumping on the head pipe. KTM was clever in routing it into the frames down tube, that way it can drool out on the ground and bypass the hot exhaust!

Another good tip in this area, remove the tank and use self sticking aluminum foil under the tank to stop engine heat from penetrating the lower tank and heat the gas./

Vent Hoses: My 400 EXC had been fairly trouble free so I had not dwelled on this, recently spent a day on an 03 EXC RFS and we where slopping in mud. The engine had tried to die once in a stream crossing and I had read several posts about vent hoses and was thinking about them. I had also noted the ones on my ’01 ended about the swing arm pivot, on this 03 they hung at least six inches below the bottom of the chassis. My gloves where totally gorped with mud so when we rode into a wide shallow river, not even up to the pegs, I said “good opportunity to wash that glove”, I stopped, idling in neutral and bent down to rinse the glove. The engine died, would not restart, I had to push out of the stream, then waited for the bowl to refill and use the choke to start it. Tip is as it needed the choke to start the bowl was empty, obviously what is happening is not water getting into the carb, rather gas can not get in without pushing displaced air out and the pressure difference is not adequate to push the water aside to let that air out. This is a bit like putting your finger on a soda straw, then pulling the straw out of the soda only in reverse.

Later at home I ran a test, started the bike and let it idle on the stand, I took a cup of water and held it under the bike dipping all of 4 the vent hoses into the water, in a few seconds the engine died. Then I bought on of those $19 aftermarket kits that is supposed to fix this. Anyway they believe the cure is to vent “up” rather than “down”.

Looked at the stock setup of two “T’s” and four vent hoses (plus on drain hose) and determined somebody at Kehein is nuts? (In their defense the reason Keihin likes these tubes hanging down as it reduces the risk of drooling gas on a upside down bike causing a fire.)

I looked at the $19 kit which includes an mini air box & filter to put in the air box, thought is was overkill and if the hoses are just run up I have a concern that if the bike lays on its side the vent hoses could spill gas on a bike tipped more than 90 degrees. After soaking up the info that was in the kit I tossed it. Of the five hoses one is a bowl drain (from the bottom of the carb) which we can ignore, four are vents, come from the upper part of the carb. If I may number these vents;

#1: Comes from the side of a “T” on the left side of the carb and goes down.

#2: Comes from the top of a “T” on the left side of the carb and goes up, over & down the right..

#3: Comes from the side of a “T” on the right side of the carb and goes down.

#4: Comes from the top of a “T” on the right side of the carb and goes up, over & down the left.

Also on the float bowl screws there are two tabs to retain downward hoses.

Dave’s Way;

#1: Is left alone.

#2: Is run over the top but shortened and run into the right side “T” thus negating #4.

#3: Is run up into the air box and with a small piece of tubing spliced on the hose you have left over from #4 and goes to the bottom of the air box. My preference is to pinch it between the air box & the air filter to secure it there!

Then I tossed the right side tab, Hose #1 can run thru the left one.

Now if the bike is in water the bowl will still be vented via the top hose, and if the bike is upside down and you ran the hose to the bottom of the air box it should not let gas run out. If you let it end at the top of the air box gas can run out, get on the exhaust as you stand the bike up creating some risk of fire.

Other options here, I have heard of aftermarket filters and or check valves to put in the hoses, for hose 1 still down in the water that can not be a bad idea,

Idle speed! You must set it faster than your common seat of the pants level! 1800RPM is proper for KTM’s RFS engine, any slower and your “automatic decompressor” is still activated which cuts your power in half (until the RPM exceeds some level such as 1500RPM). Additionally it is more primed & ready for the quick acceleration and as you turn the idle speed up you will find the bike jumps and goes thru whoops flatter rather than nose diving. A low idle makes the nose dive into every hole and the bike becomes a handful to ride.

Float Level: You have fixed a toilet, right?? Fairly simple deal we have fuel in the line, gravity trying to feed it in (toilet has water pressure to feed it) and a valve called the “needle valve” trying to hold it out. Now we need to stop and talk about definitions, the “needle valve” is just that a valve. The “needle” we talk about in the jetting section is totally different, its real name is “jet needle” (but if you say that know body knows what your talking about).

The float has a tab on it that as the fuel raises the float floats up and at some preset point that tab presses the “needle valve” into it seat and stops the fuel flow. This becomes the “regulator” of the fuel level, thus the name “float level” is really addressing “fuel level”. Now a couple points we need to understand about the “fuel level”, as the fuel is siphoned up thru the jets the higher it has to lift it the lesser amount of fuel is going to go thru the jets. Thus you could have jet sizes that where known to be perfect for your model bike, but a higher than standard float level could make it run sloppy rich, a low float level would make it run lean. Thus a given amount of air siphoning from a;

Low float level is going to siphon less fuel/run lean OR a

High float level is going to siphon more fuel/run rich.

If your working with a bike that has a few years on it and especially if hauled on a bouncy trailer that float level may have raised from the wear on the float, its hinge, needle etc.

The manufacturers always give you some spec, it may be “level” (carb upside down) or 17mm or whoknowswhat? That made sense to me way back in the dark ages as the “needle” was a solid piece, you lift it up and the fuel shut off at one precise spot. Solid piece needles went away in the early ‘70s as when your bike went thru bumps the float bounces, fuel was on off on off etc the float level went too high and the engine ran rich until you slowed down (the bikes gave us lots of frustrations back then). So then needles started coming with a spring in the middle of them. Float pushes on needle, needle pushes on spring, spring pushes on needle valve, fuel level is much more constant but, setting the float is a bit more weird as when the carb is upside down the weight of the float pushes it down further than the point that it shuts the fuel off!

Dave’s way; I blow thru the fuel line while manipulating the float by hand, find the point where it shuts off the air/fuel flow and record it!

Float Level: Always start with the factory spec here but some double checks are;

If the carb drips while the bike is on the side stand its way to high!

If you burn up the engine with jetting that is within normal levels it may be too low!

On the bottom of the float bowl there is an “overflow hose”!

Bump Test: I remove, set aside this hose, wipe the transmission cases clean and dry, then ride around for a minute or so, very mellow, low gear just rolling over some light bumps, no “G Force” deals, then stop and check the top of the transmission case. My theory, no gas should drool out, if it does the float is too high.

Hose test: Same hose, leave it connected to the carb but pull it loose from the bundle that goes down with the other drains. Bike upright on a stand, on the bottom of the carb there is a drain screw, (4mm allan) loosen it, so fuel starts running out, now grip the hose and turn it upwards laying it against the side of the left front corner of the carbs float bowl. The fuel level in the bowl should be the same as the level in the hose, you can mark this on the side of the bowl with a felt pen, compare to another bike etc. Mine is 8mm above the bowl gasket.

Idle circuit: The idle circuit is made up of the pilot jet and a mixture screw, the mixture screw on 4 stroke carbs adjusts fuel, thus out is rich. 2 strokes are the other way around, they adjust air and out is lean. The idle circuit is working at all times but as its volume is small it has a very limited effect in the upper ranges. As it has little effect on upper ranges your bike could run fine at full throttle with the idle circuit messed up but starting and response would be a mess.

Idle Mixture Screw: These are a bit of a pain to reach so a common cure is to replace it with an aftermarket extended one. I do not care how catchy its name is or how fast the rider associated with them is do not buy the aluminum one! If you have one toss it as it is capable of trashing your carb!

Dave’s way: KTM hard parts is Stainless, Scotts, Slaven’s & Kouba each have high quality brass pieces and I am sure there are some others.

On any of them care is required when you remove them! There is a spring, metal washer and an O Ring on them and they don’t always come out with the screw, fall out later and get lost etc. There is a siphon going on here so if the O Ring is missing it will siphon air rather than gas, thus run lean!

Assemble by holding the screw upright, fit the spring over the screw, then the washer, and lastly the O Ring.

The screw should be around 1 to 2.5 turns out from bottomed. If it wants to be further in go one size smaller on the pilot, if it wants to be further out go bigger on the pilot as if you get out 3+ turns the springs tension no longer holds it and it may just fall out on you!

Varnish: If a bike sits for months un-run the gas in the carb can evaporate which leaves a varnish reside inside. Don’t discount the possibility of this problem on a new bike. The gas run thru them at the factory has some additive in it to prevent this but its not uncommon that the dealer puts gas in it, runs it, then puts it in the showroom and the bike sits for months. Now the bike does not want to start and if started runs miserable! Two things can be effected;

A: The Pilot jet becomes plugged! This jet is so small that the varnish coating can plug it solid!. Avoid poking it with wire, torch tip cleaners are a no no, the size on this piece is way to critical too be poking stuff in it as it will be bigger afterwards.

Dave’s way;

A: Plan on removing the jet and soaking it in lacquer thinner to clean up the pilot. Lets not clean “all the jets”! First its pointless and second you likely to cause more damage then good, and please don’t take the slide out!!

B: This varnish can not only plug the pilot jet but the AC pump has two tiny check valves in its system. Either of those can be gummed up rending the AC pump useless. One check valve is in the bowl, will look like a ball bearing in a hole in the bowls bottom, the other is up inside the body of the carb and un-serviceable. Either of both of these can become stuck with this varnish and the AC pump will either not work or not work up to par. It may free up in time but the rider may hate waiting!

Dave’s way; Plan on removing the bowl, removing the AC pump diaphragm (careful of the small parts) and set it aside. For the lower check valve, soaking the bowl in Lacquer thinner for a few hours, take your partners tooth brush and scrub the green stuff out of the inside, then with a small blunt ended punch and with the bowl submerged stroke the check valve ball up and down and the lower check valve should be good to go. For the upper, there is a passage from the bowl to the carb body near the rear of the carb body. Additionally its possible that the AC pump squirt nozzle plugging, rare but possible. Plan on getting the carb upside down and pouring some lacquer thinner up that hole.

When re-assembled before installing, fill the bowl with gas, hook up the throttle and give it several twists to purge the air out of the system, then twist the throttle to check the squirt, it should start promptly with the twist and while a small stream should continue steady for some pre-determined period. See Accelerator Pump Set Up 101 for modifying the squirt for specific applications.

Water: Occasionally in winter conditions we get water in the gas. You have seen how water mounds up on the drinking fountain. This is from what is called “surface tension”, do to this surface tension, the tiny size of a pilot and the small amount of vacuum of the siphon effect at the jets water will not flow thru a pilot jet! Its plugged yet clear when you remove it for examination.

Dave’s way; In the winter, or anytime a plugged pilot is suspected, toss a couple ounces of rubbing alcohol into the gas, this and water are each is heavier that gas so they go to the bottom of the float bowl, the alcohol breaks the surface tension of the water and both pass harmlessly thru the jets and is burned away.

Off idle thru ¼ throttle: As you open the throttle you transition from idle circuit being the shank of the needle (straight part).

1/3rd to ¾ throttle: This range is controlled buy the taper of the needle and its relative location controlled by a clip at the top of the needle.

Full throttle: In a perfect world this is controlled by the main jet. The reason I said “in a perfect world” is in order to be imported into many counties KTM had to fit a needle that has very little taper. Due to this low taper angle the needle blocks the main jet!

All those specs: Jet sizes are metric, a #42 pilot is 42% of a mm (about .016”). a 170 Main jet is thus 1.7mm or about .068”.

Needles: There is more info on the Sudco web site but in a nutshell, the needles made by Kehein have five letters. Kehein uses this same series of needles on all from 37 to 41mm carbs OBDTM is an example.

First Letter “O”: is going to apply to all of the carbs it fits, nothing we need to dwell on.

Second Letter “B”: is the material, (no need to dwell on it)

Third Letter “D”: Is taper angle, Kehein gives us two reasonable options “D” & “E”; I call these “D series” and “E series” etc.

“D series” Very little taper, its best use is for emissions approval, import certification. On the 37 & 39mm carbs its tip is blocking the flow of the main so I am not to fond of it, in a 41mm such as the 450 & bigger SX/SXF it is OK. On a 39mm such as the XC line it should be tossed as the needle is so blunt towards the tip that it blocks the flow of the main jet! This has been standard in all KTMs from 00 up to the new twin cam 250’s which have an “E series” “E series” Has a lot more taper, as main jet blockage is no longer a factor it needs a smaller main.

Fourth Letter “T”: It is more complex but a simplified version is the distance from the clip to start of taper, we need the Keihin Chart to compare.

Fifth Letter “M”: Is the shank. The Shank controls the off idle thru ¼ throttle range, if this range is not happy nobody is happy! The basics are, each letter down the alphabet is one step (1/10th of a mm) leaner than the letter before it. Exception, they skip “O” (oh) as it is too easy to confuse with “0” (zero). Thus each of these is one step leaner then the preceding one, “M”, “N”, “P”, “Q”, “R”, “S” is the range we are concerned with.

Dave’s way; Two options here:

1: Is the JD needles, they are a bit more complex as it changes the taper angle mid way and are between the two Keihin needles. They are tailored for the bike rather than just picking thru what Keihin makes and performance is the goal rather than emissions or picking thru what is available. With this you get JD’s development work on the specific model, dyno, exhaust analyzer etc. and quite a bit of seat time development, BTW he rides a 450XC. One word of caution, his kit assumes he is fixing the combo from stock. Say your dealer swapped from a #42 pilot to a #48 to try & fix the factory “lean” needle. JD kit assumes you have the #42 and fixes the lean condition with the needle. If in doubt, consult your manual, compare what was originally specked out and what you have, in the above example you would want to order that #42 pilot separate from the kit.

2: Sudco is the importer of Keihin parts, your on your own but for the KTM 400-525 a OCEMP with a 162 main is a pretty workable combo. Do to the step taper this combo is richer in the ½ to ¾ throttle range then the JD. If you spend a lot of time flogging in sand dunes consider this combo!

The Transition: This is when we first do the twist. As we ask the carburetor to go from idle mixture to needle. You will have a better throttle response with a lean idle to rich needle transition then you can with a rich idle to lean needle. This is part of why I discourage trying to fix the factory lean fuel mixture with a big pilot jet!

Some resources

Setting the start of the squirt http://www.pbase.com/jdjetting1/image/50507859

BK Mod Instructions: http://www.ledametrix.com/bkmod/index.html

BK Mod Instructions: http://motoman393.thumpertalk.com/tech/carbpics.html

BK Mod Instructions: http://www.4strokes.com/tech/ktm/crockbkm.asp

Diagrams/parts: http://www.sudco.com/fcrside_diagram.html

Fuel Screws http://www.koubalink.com/fuelscrew.html

Fuel Screws http://www.slavensracing.com/products_ktm.htm

Fuel Screws http://www.scottsonline.com/

Tech http://www.thumperfaq.com/ap.htm

Slide Plate http://www.pbase.com/jdjetting1/image/25566144

Jet kits, float bowls etc. http://www.jdjetting.com

Kehein needles chart http://www.keihin-us.com/needle.htm

Also read AC Pump 101

About the author

Dave Hopkins is a former Husky dealer, former off road competitor and mechanic, today sells Real Estate in the Seattle area and as a hobby business does head work on MC cylinder head primarily KTM & Husky. Can be reached at davehopkins@windermere.com

  • Like 2

Share this post

Link to post
Share on other sites


(For the Keihin FCR Carb)

Note do to the complexity of the accelerator pump I have broken this into two sections, Carb Set Up 101 and Accelerator Pump Set Up 101

First lets understand the basics, a carburetor works on the principle of air flow siphoning gas as it passes the needle & jets. At idle the air flows thru a very restricted area adjacent to the jets. When you twist the throttle quickly at low RPM the air flow is suddenly moved from right at the jets to spread over a big area, same amount of air spread over a larger area, vacuum decreases and air speed at the jets decreases too the point that fuel siphoning stops, no fuel equals Bwaaaaaa!

To supply fuel from the “twist” until vacuum is restored the manufactures have several options;

1: Smaller carburetor.

This keeps the air flow close to the jets, makes a bike work nice in low speed maneuvering but kills top end power!

2: Fuel injection.

This it does not rely on the siphoning effect. Like it or not it’s coming as;

A) As they are not vacuum dependant they can use a bigger throttle body thus Rev higher equals more power, and

:ride: Once the R&D work is done and you turn up production volume it may cost less to produce than a carburetor.

3: Constant Velocity (CV) Carb:

A “CV” carb is an excellent deal, you whack the throttle open (or think you did) but a vacuum controlled deal keeps it only part open until the engine is revved up enough to use it. Common on street bikes, to put one on your KTM you would have to cut a notch out of your knee to get the space and get stronger springs as it would add several pounds. Not suited well for a “race bike”.

4: An accelerator pump:

This is the route most of the state of the art off road bikes have until we get FI, this provides a little shot of fuel to fill in during that moment of lag in vacuum. Problem is how much gas? Earlier designs squirted gas “while” the throttle was being moved, once the movement of the throttle stopped the squirt stopped. That was a bit too brief and left many a car or MC pre-igniting (Pinging) for a moment after the “twist”. This Pinging can lead to a piston failure! The common setup on the Kehein carb is set to squirt for 3 seconds after the twist. This is not necessarily wrong, just a compromise setting chosen by the manufacturer. What we need the AC pump to do is bridge the gap from the “twist” to the engine being revved up a bit, lets just guess that 3,000 RPM will be enough to get the air flowing sufficient to get the siphon effect underway again, while a big twist at low RPM can make the engine “fall on its face” even once past that point a heavy load on the engine the engine could be experiencing a lean spot that can lead to pre-ignition.

We could debate names all day but in my definitions:

A: “Lean Bog” is when lack of vacuum to maintain the siphon effect has caused the engine to run out of gas before the RPM got up to where the siphon thru the jets can take over. The AC pumps job is to bridge this gap, and

B: “Throttle Stall” is when too aggressive of an AC pump floods the engine.

The area in between is the Happy Zone we all strive for, the manufacturer does not know how your going to use your bike but they do know, not enough AC pump can cause pinging/piston failure, too much AC pump causes a bog, which is worse? So they have to seek a compromise combo on the AC pump.

Most off road riders are using relatively low gears, this together with wheel spin gets the RPM “up” quickly!

Example 1:

You have left camp on asphalt headed for the trails, riding pretty mellow, think your being easy on the bike, exit a corner at say 1,500 RPM in 5th gear, you roll on a little bit of throttle and the engine slowly builds momentum so its 3 or 4 seconds before the engine gets back to 3,000RPM. What would happen here is without squirt of the AC pump the engine would be very lean yet with a fair amount of load on it, several seconds of that “easy treatment” may even be melting away a small bit of the piston. By designing an AC pump that continues squirting for say 3 seconds that lean spot is patched over by this “squirt”!

Example 2:

A bit down the road you turn onto a trail of delicious loamy soil, you whack the throttle open and the rear tire breaks loose, the RPM jumps almost instantly into its happy zone, say to 5,000RPM and while the phun meter heads up yet the engine seams just a kinda hang there a couple seconds, then takes off! What is happening here is when the RPM jumped up the air flow thru the carb drew in all the fuel the engine needed for its proper fuel air mixture thru the jets! Yet at the same time it was being supplemented by the AC pumps squirt. Combined the two fuel supplies and the fuel air mixture was overly rich, that “rich” mixture burns slower than a correct fuel air mixture and the engine feel just a bit lazy.

Example 3:

Your on your shinny new Orange bike and leading your buddy who rides this wrasspy old “faded old blue” bike, you enter a corner with this MX track like berm, your leaned over maybe 60 degrees and you whack the throttle open anticipating roosting old blue, you anticipate “Rriiiiippp” but hear “Bwaaaaaaaa”, engine dies, 60 degree lean angle becomes 90, phun meter collapses. Old blue’s owner gives you some squidly look. What happened here is your AC pump was set for example 1 and basically flooded the engine!

These “High Performance Engines” have a carburetor that is big for its size so they do not maintain vacuum when wide open so it needs that AC pump squirt to fill the gap of the "lean bog". Often the AC pump is set up too aggressive and floods the engine, the “throttle stall”.

Kehein was very clever in this design as it squirts during the twist AND for some predetermined amount of time after! First and foremost your pump needs to be working!

Check for

A: Function! It must squirt when you twist

B: Start of squirt! It must squirt as quickly as the slide starts moving up but should not splatter on the back of the slide!

C: Duration! The duration is the amount of time is continues to squirt after the twist!

Start of the squirt;

On the 03 and newer models there is a screw on the right side of the carb that adjust the start of the squirt, when correct the squirt does not hit the slide, the slide should lift and the squirt follow just under it. The following link gives you a good starting point:


Duration of the squirt:

Most bikes as a compromise are being supplied with the AC pump set to squirt for 3 seconds after you twist. If your riding is strictly off road the bike can be more responsive by shortening that duration! Do Not reduce this squirt duration on any bike that is used in high traction riding such as Dual Sport! You can’t have it all and trying to make one of those bikes respond like a moto crosser would make it deathly lean when you gently rolled on a little throttle on asphalt!

You have to judge how long of squirt time you need! That is tied to how low or high of gears you use, wheel spin, gearing, size of bike etc. If you are a very passive rider, roll on the power gently and seldom spin a tire the factory 3 second setting may be prefect. However most off road riders are geared down for the woods and ride aggressively so the low gearing and wheel spin will have the RPM up in about a second, thus they want a 1 second squirt time.

Pay close attention, test to follow! The way the AC pump works is very clever in that the throttle activates a link pushes a spring that pushes a second link (you gotta look at it) that allows the second arm to be delayed, the delay is caused by the fuel pressure in the pump circuit! To illustrate, visualize yourself draining a hot water bottle full of water, you toss it into the sink, pop the cap off and press on it. What happens parallels when you twist the throttle, the throttle door that controls air is allowed to open right up but the hands pushing on the water bottle takes some period of time for the water to squirt out!

On the carburetor this creates a squirt that in stock setup is for about 3 seconds after you twist, we can reduce the squirt by blocking the pumps movement OR by leaking off some of the fuel pressure! Like draining the water bottle we can vary how long it takes with pressure, or by stopping the push! Stopping the push on the diaphragm is achieved by a mechanical stop, a bit like tossing a rock into that water bottle so you can’t squeeze all the water out:


1: Honda Mod: Kehein makes a series of different AC Pump diaphragms with a post on the bottom to stop the diaphragm just as the rock did in the hot water bottle. Basically the longer rivet thru the middle that stops its travel, the shorter the squirt. My recollection is that there are 4 lengths available? The KTM comes with the shortest post, longest squirt. The “Honda piece is the longest post, shortest squirt.

The best part is this works on all years of the Kehein FCR carb, is a simple, no brainer, minimal talent required just change the diaphragm, if you buy from;

Honda, you get a couple other pieces with it that you can ignore a bargain at under $20 (Honda allegedly owns Kehein so they can sell parts for less). Honda’s number is 16021-MEB-771, or

Yamaha, price is a bit higher I think close to $30 but there is some in between lengths available

part # 5JG-14940-19-00, (9mm post) would be the same as the Honda (short squirt)

part # 5JG-14940-18-00, (8mm post) a little longer squirt

part # 5JG-14940-76-00, (7.5mm post) a little longer yet

part # 5JG-14940-17-00, (7mm post) a little longer yet

part # 5JG-14940-16-00, (6mm post) I believe same as KTM

2: BK Mod: For ’03-05 only, you drill & tap a hole, install a screw & spring to make an adjustable stop called the “BK mod” (Brian Kenny). The link to its instructions are near the bottom of this page. For the bikes that it works on this is my choice because its almost free and fully adjustable.

2.A: For the ‘00-02 bike you do the same thing by bending a tang on the side of the carb, it is like a small fork and you need to bring the tips closer together, then recheck. For a pic go to JDs web site photo gallery, currently it is page 3 (but that may changes as more photos are put on the site?) http://www.pbase.com/jdjetting1/keihin_fcr_pictures&page=3 look for photo titled Pinched_Linkage.jpg

3: Taffy mod: This involves a wheel spacer from some model airplane that is slipped over the rod of the AC pump, while this is perfectly viable and I believe works only on 03 & newer, I have no further info.

4: I have also heard of gluing a valve adjustment shim into the bottom of the AC pump cover, someone even did this with a button but that can trash a good shirt.

5: And threading a hole in the cover and putting in a set screw adjustable stop! I like this with the exception of fear of gas leaks.

6: There is an AC pump cover called a P-38 that also restricts the pump travel, probably just fine but much more money the make one of the simple adjustments above.


A: “Leak Jet”: As the AC pump is pumping more fuel than we know what to do with another way to reduce the squirt is via a metered leak back to the float bowl! Most of the bikes other than KTM have a “leak jet” in the float bowl, up thru 05 KTM did not have the hole machined for it, rumor has it that some 06’s do?? If not you can by a bowl from JD that is machined for the jet. Common jet sizes are in the 50 to 80 range. What this “leak” does is reduce the fuel pressure of the squirt! As the duration of the squirt is tied to the volume of fuel pressurized under the diaphragm adding a leak quickens the draining of that chamber. Thus adding a leak shortens the duration somewhat like that of mods 1-6 above. BACK TO THAT WATER BOTTLE, ADDING A LEAK JET IS LIKE HAVING A SECOND NOZZLE ON THE OTHER END OF THE BOTTLE (ONE END GOES TO ENGINE, THE OTHER END GOES BACK TO THE BOWL.)

Leak jets can be had thru Yamaha dealers, the size is a percentage of a mm in diameter and as this is not ultra critical I am not opposed to drilling jets when needed.

#40 –s 4JT-1494F-03-00

#50 –s 4JT-1494F-07-00

#60 –s 4JT-1494F-11-00

#70 –s 4JT-1494F-15-00

#80 –s 4JT-1494F-19-00

#90 –s 4JT-1494F-23-00 (there are more but somewhere around here the pump is disabled by the leak)

B: Wire Mod: I am deleting this as it caused confusion and in my mind the idea lead too but has been superceeded by the O Ring mod below. If you have the wire mod its time to switch.

C: ORing Mod: 03 & newer only! Credit for this twist goes to JD as a modification of the mod by Redbeard. This involves taking an Oring (JD sells a kit) or an ID about 5/16th inch and OD about 7/16th inch and installing it around the two black arms.

Many paragraphs back I said there would be a test! And described how one arm pushed on another with a spring, well this ties the two pieces together with a bit of elasticity which increases the pressure of the spring, thus increasing the fuel pressure of the pump for its initial hit! This yields a higher volume initial hit, then the pressure tapers off. I personally watched & road tested this on a KTM 525 and it brought this bike to life! It worked very well in conjunction with a limited travel diaphragm of mod #1!

D: Quick Shot: This does the opposite, it increases the squirt. Its purpose appears to be for some bike (that I have not met) that needs a stronger squirt than original. For the rest of us I see no value in the piece, I have heard that some have benefited from its instructions on setting the start of the squirt which are free here so just take the $94 you just saved and send to me:>) & I will try to find you some old decal.

E: The DJH mod: I have been drilling out the spray bar of the AC pump, effect is about the same as the Oring mod except there is less pressure applied to your arm, better for long days. This is brainsurgery delicate so I am not going to offer spec & such.

250SXF Has trouble using the full volume of fuel of the pump, is easily flooded when stalled and at least in a trail application favors a softer hit of the pump (reduced fuel pressure) AND the reduced duration. Thus my recommendation is BOTH mods “#1” and “A”. Side benefit, this will help if not cure the hard starting when hot problems we see at the MX races.

Street, Dual Sport who have 100% traction need the more duration then off road, maybe the full 3 seconds? Too short of duration can hurt your engine when riding mellow. If pre 06 you might try Mod #2 as its adjustable and tinker with it out on the road? Listen carefully for pinging and run as long of duration as you can without bogging.

Motard or Ice racers may have the 100% traction but are less likely to gently roll on the throttle, more apt to be revved up all the time? So I suspect a short duration is fine?

Some resources

Setting the start of the squirt http://www.pbase.com/jdjetting1/image/50507859

BK Mod Instructions: http://www.ledametrix.com/bkmod/index.html

BK Mod Instructions: http://motoman393.thumpertalk.com/tech/carbpics.html

BK Mod Instructions: http://www.4strokes.com/tech/ktm/crockbkm.asp

Diagrams/parts: http://www.sudco.com/fcrside_diagram.html

Diagrams/parts: http://www.keihin-us.com/needle.htm

Fuel Screws http://www.koubalink.com/fuelscrew.html

Fuel Screws http://www.slavensracing.com/products_ktm.htm

Fuel Screws http://www.scottsonline.com/

Tech http://www.thumperfaq.com/ap_mods.htm#HB

Tech http://www.thumperfaq.com/ap.htm

Slide Plate http://www.pbase.com/jdjetting1/image/25566144

Jet kits, float bowls etc. http://www. jdjetting.com

Another way to look at this accelerator pump deal;

Think of this as sitting in a very small room with a 400 watt light bulb hanging over your head. You get a headache, right? So:

Quick Shot is like getting a 500 watt bulb, and a decal but its heavily advertised.

Honda Diaphragm is like getting an 80 watt bulb (probably just right and you will probably never think about it again.

BK mod (which only works from 03-05) is like having a dimmer, your probably going to dim to the 80 watt level but you can adjust as you like.

O ring and DJH mods are like having the 500 watt bulb and a dimmer, you switch it full on then immediately turn it down to a tolerable level.

Also see “Carb Set Up 101”.

About the author

Dave Hopkins is a former Husky dealer, former off road competitor and mechanic, today sells Real Estate in the Seattle area and as a hobby business does head work on MC cylinder head primarily KTM & Husky. Can be reached at davehopkins@windermere.com

  • Like 1

Share this post

Link to post
Share on other sites

Checking/Monitoring the Valve Clearence

SXF Engine

On this engine several procedures are going to be different than the RFS, checking is simpler, changing is more complex than the RFS but the object is, this is a “Race Engine”, designed to withstand higher RPM than the RFS is and that together with advantages that I kind of understand but not really qualified to explain about the radius of the cam followers contact with the cam, small radius allows valve lift patterns that can not be achieved with the “shim & bucket” design on the Blue bike that has allowed KTM to achieve more power.

The factory specs (cold engine) are:

Intake .10mm to .20mm (converts for us that think in inches to .004” to .008”), and

Exhaust .12.mm to .22. (converts to .0048” to .0084”. lets call it 5 to a loose 8).

Tools, In addition to common shop tools you are going to need;

1: Feeler gauges in several thicknesses above and below the spec! While bent ones are preferred on the RFS on this engine I prefer a conventional gauge. On the RFS we where only concerned with the setting when done so we only needed one gauge, here we must know what it was! So we need a few such as .003 thru .009”!!

2: When we get to changing shims we are going to need a long skinny magnet.

3: When we get to selecting shims you should have a micrometer.

4: We are most likely going to need some replacement shims. They are 8.8mm in diameter and range from 1.72 to 2.60mm on steps of .05mm. Cost is about $5 each.

Checking the valve clearance:

Remove fuel tank, clean any debris around the valve cover.

Remove the 4 bolts that attach the valve cover and slide cover out to the right (it is tapered to make it easier to go right)

Intakes (rear pair)

1: To check intakes, rotate the engine until the Intake (rear) cam lobe is near straight up.

2: Under the cam lobe there is an arm (“finger follower”) that makes up the space between the lobe and the valve.

3: The point you need to measure is between the finger follower and the tip of the valve. 4: Select your feeler gauge, and thru trial & error find out what the clearance is! And then keep records!

5: So starting with the left rear, check with various gauges until you establish what gauge fits with some drag.

6: Lets use for example it was .004” so we are going to start a record of LI (Left Intake) = .004”. Next repeat on RI and lets say it was a 5 so we record RI = .005”

Exhaust (front pair)

To check exhaust, rotate the engine in its forward direction until the Intake is mid stroke closing. At this point the Exhaust (front) cam lobe is near straight up but if you go much further the automatic de-compressor will briefly lift the exhaust valves very slightly. IF you find you have zero clearance back the engine up slightly!

Repeat 1-6!

So when complete we have a record something like

Bike new, 5 hours use. Or bike purchased used time unknown.

LI = .003”.

RI = .005”.

LE = .006”.

RE = .007”.

I want you to save that record permanently! Now if those where the numbers your bike has you are within spec and no need for any adjustments. However when we do need to make changes we want to record all shim changes! The reason is we want to keep track of how much each valve has stretched and or seceded into the valve seat from new! In time we will learn more about when the valves need to be “cycled out” to catch them before they fail and damage the engine.

An example would be when you have changed the shim on a valve more than say .005” then its failure is eminent so change it now while it’s a cheap repair.

This is a bit like a Top Fuel Drag car throwing away a $3,000 crankshaft at 12 runs because they know between 15 & 25 it will break and do $50,000 in damage not to mention danger and lost competition.

In our case its more like a $100 valve and $2,500 damage & pushing out of the woods. Still running a valve that has stretched/seceded into the seat to a point approaching failure is not cost effective.

As spec is .004 to .008”

LI = .003” so we need to reduce the shim by .001”

RI = .005” OK.

As spec is .005” to .008”+

LE = .005” OK

RE = .005” so we need to increase the shim by .001”.

What I want you to do is AS YOU CHANGE SHIMS maintain a record something like this.

3 hours 25 hours 40 hours total

LI = --.001”, --.002”, --.003”, .006”!*

RI = --.000”, --.001”, --.002”, .003”!

LE = --.001”, --.002”, --.000”, .003”!

RE = --.001”, --.002”, --.001”, .004”!

Based on input from a valve manufacturer I am guessing that .005” will be a safe operating range so in the case of the record above I would be changing at the minimum that Left Intake!

ADJUSTING THE VALVE CLEARANCE: I recommend that you have the KTM Shop Manuel in hand before diving in here!

The concept is we have to change shims that are in the center of the valve spring retainer. Shims are available from KTM from 1.72mm to 2.6mm in .04 mm graduations. Establish how much we need to change each and write it down, then:

1: Turn the engine to top dead center, piston up, both cams lobes near up! Check that the two crank gears have punch marks on their left side facing each other and perfectly aliended with the mating surface of the caps that retain the cams!!!

Install the top dead center lock down bolt in the bottom of the case so it is engaged into a notch in the crank.

2: Remove the cam chain tensioner (Right Front corner of the head).

3: Remove the two bolts that hold down the black chain guide that is above the chain, set the guide aside.

4: Remove the remaining bolts holding the cam bearing caps, set them and the bearing caps aside

5: lift the rear cam and allow it to roll forward within the cam chain as you lift, once it has come forward the chain is loose and you can slide both cams out of the chain. Set them aside;

Go to valve;

LI measure the existing shim locate and replace with one .001” thinner (or whatever was needed)

RI was OK so leave it alone

Repeat until all adjustments are complete

Note, if you need a shim say .001” thinner and do not have that shim you can lap the shim on a piece of fine sandpaper, check with a “mic” to determine when you have removed that .001”. If there is a number etched into the shim to state its thickness we may as well do that side of the shim as the number is now wrong (you may hate yourself for having done this next time around).

Reinstall cam without chain, roll so lobe is up and re check clearance, repeat if necessary.

When satisfied reassemble, the punch marks on the cam gear must point at each other and match the mating surface of the bearing caps! The torque specs for the bolts holding the cams in place is 18NM.



The timing chain tensioner operated with spring force and with oil pressure. A stop system is used to ensure the right amount of chain tension in the starting phase, even if the oil pressure is insufficient. The stop system prevents the piston on the timing chain tensioner from being retracted. In a dismounted state, the piston on the timing chain tensioner extends completely.

Fully depress the spring tensioner. This will require some effort since the oil must be squeezed out. If the timing chain tensioner is released it will extend completely again; it may not be mounted in this state, since the locking mechanism will not function.

Press down on the timing chain tensioner to ensure smooth operation.

To prepare the timing chain tensioner for installation, place 2 washers or similar spacers with a thickness 2 to 2.5mm (two nickels, one each side of the tensioner in between is perfect) next to the piston of the timing chain tensioner. This will ensure that the piston can not be completely retracted when the piston is pressed down. If you release the piston, the stop system will lock, the piston will protrude approx 3mm and stay in this position – this position is mandatory for refitting!

If you press the timing chain tensioner again and it extends no more than half way (preventing it from extending completely), the stop system will “lock” and the timing chain tensioner can go no longer be pressed together – this position is necessary to ensure that the timing chain is adequately tensioned, even if the oil pressure is low.

Slip the hydraulic tensioner into its hole the telescoping end first, install the plug with its sealing ting and tighten to 25NM.

Then with a substantial screwdriver enter it into the RF corner of the head, straight down just forward of the cam chain, get the tip of the screwdriver on the front side of the black tensioner bar and force it back against the chain to “relieve” the previously “locked” tensioner so it can hold the chain tension firm until oil pressure takes over!

Caution! The tensioner must be applying tension!!! If the chain tensioner is not “relieved” after assembly as described above, the timing chain will skip when the engine is started resulting in valve damage.

Do to fear of folks botching the cam chain tensioner and destroying their engine based upon my instructions I am referring you to the KTM manual for any changes in valve adjustment

  • Like 1

Share this post

Link to post
Share on other sites

Valve adjustment

KTM RFS engine

Please pay attention somewhere KTM has printed a manual that says something to the effect you should adjust valves at “Top Dead Center” AKA “TDC” the point where the piston is up. The movement of the piston is controlled by the crankshaft, the crank turns the cam shaft at ½ crank speed and on a 4 cycle the valves are controlled by the camshaft. Thus when they said TDC they lost something in the translation of languages, one TDC is OK to adjust, the next one both valves are very slightly open. Goal here is to forget TDC, forget dropping pencils into spark plug holes and just adjust the valves!

Clearance: To allow the valve to fully seat and transfer the heat it accumulated when open, and to allow for heat expansion when hot, the camshafts lifting pattern and valve train are designed to operate with “clearance” “lash” or “gap” between the valve train and the valve. Too much clearance and the cam and cam followers are prone to wear out. Too little clearance and it can burn a valve, or if you are lucky just not start at all so let get it right. KTM has a service bulletin recommending that we ignore the prior specs and set the valves at .12mm which in inches translates to .005”.

Rotation: Note that the engine rotates the same direction as the wheels and that when we rotate the engine we are fighting the valve springs, the easiest way is to put the transmission in top gear, this gives the wheel max leverage against the engine, conversely to how 1st gear gives the engine max leverage against the wheel. Then we rotate the engine by the rear tire. If you want to avoid pulling the spark plug out you can, just hold the manual compression release while turning the engine.

Getting to it: First remove the seat & tank, from there I have done it radiators on, and hated every minute of it, I have done radiators off, it is more labor but maybe less maddening? (On '03 try setting the radiators aside without disconnecting the hoses) Unless the bike is spotless I like to take a can of Brake Clean and someone else’s toothbrush, spray & scrub the valve covers and the area around it, then spray the area around the spark plug with the brake clean to flush out that area. If you have compressed air a good blast would help clean debris out of this area but watch you eyes! Then remove the valve covers and if you are going to the spark plug but if you do it my way there is no need on the plug.

Now we must locate the “heal of the cam” where the valve lash is to be adjusted.

My way: With this method you do not need to remove the spark plug, magneto cover, skid plate or the TDC bolt in the bottom of the crankcase or the associated dirt.

Intake valves; (carburetor side of the engine) Transmission in top gear, rear wheel off the ground, if you have a helper one can watch the valves and hold the manual compression release while the other rotates the engine with the rear wheel. Rotate the engine gently with the wheel to locate the point where the exhaust valve starts to open then rotate very gently until the exhaust valves are 1/2 way open (open is down)! Minor frustration, we are now fighting against the valve spring which wants to roll the engine back, so to stop it get your largest screwdriver, slide it thru the spoke of the rear wheel adjacent to the swing arm to lever the wheel/engine back or forward to the correct spot. At this “exhausts ½ open” point the Intakes are on Center of the Heal of the Cam. Proceed to adjust.

Exhaust valves; (front side of the engine) As above, except, locate the point where the intake valves have opened (open is down) and are 1/2 way closed (engine rotating forward). As the intake is closing the engine will want roll forward PAST the ½ way point and the lash in the transmission and chain will make it so you can not stop the engine, so let it go just past, then roll the wheel backwards and secure it with the screwdriver or bar again. Now proceed to adjust the Exhausts.

ALWAYS! ALL 4 STROKE ENGINES: With the engine rotating its correct direction the exhaust is adjusted when the intake is closing and the intake is adjusted when the exhaust is opening!


If you are a “feeler gauge” kinda guy; As the clearance is so small and you can not get a straight approach with the feeler gauge don’t be surprised if you can not get it in. I like to loosen the jam nut (10mm box wrench) and loosen the (one at a time) adjuster a couple of turns, slip the gauge in, turn the adjuster down lightly against it, then tighten the jamb nut. In doing so often the adjuster will creep tighter slightly and cause the clearance to close up. What you need to do as you tighten the jamb nut is do kind of an isometric exercise where you are holding the adjuster against rotation with equal and opposite force of the rotation of the jamb nut! This may take several practice attempts. As soon as you have tightened the jamb nut, do not pull the feeler gauge out, just try to slide it around in the gap! When you have it right it should slide with some, but minimal drag or resistance, no drag and it is too loose, heavy drag and it is too tight, may even be holding the valve open? Take a little time, you will have to redo a few times at first but once you pull the gauge out you may not be able to get it back in so get it right first! Oh, and by the way, the jamb nuts need to be tight!

If you are a 1/6th turn kinda guy; I think it was the Husaberg guys that came up with the theory that fraction of a turn will do! The “Bergs have a different thread pitch, I think they use 1/5th of a turn? My first reaction was that is crude, then I tried it a few times, now do it every time. That is based on a turn equates to .75mm (on the KTM tread) and .75 div by 6 = .125mm and .12mm is spec so for all practical purposes 1/6 turn is right on! Loosen the jam nut (10mm box wrench) and very lightly tighten (one at a time) turn the adjuster in until it lightly contacts the valve, note where the screw slot is aimed, turn the jamb nut to a corner of the hex aliens with the slot, make a small scratch in the cover gasket surface in line with the next hex point left (hex being 1/6th turn to the next point). Then turn the slot to that point, then tighten the jamb nut. In doing so often the adjuster will creep tighter slightly and cause the adjuster to tighten up. What you need to do as you tighten the jamb nut is do kind of an isometric exercise where you are holding the adjuster against rotation with equal and opposite force of the rotation of the jamb nut! This may take several practice attempts. As soon as you have tightened the jamb nut just double check that it did not creep, the slot aimed at the mark we made 1/6 turn left of contact and move on the next valve.

The jamb nuts need to be tight and there are a couple of ways to deal with it;

1: Get out the torque wrench, check the factory spec and torque it down. Problem is with that is your locked into using a socket so you won’t have the screw driver resisting movement of the adjuster, if the torque was close it should be OK. If it turned the nut much it may creep the adjuster around and changed your clearance setting. Thus what you have to do is be very close by hand before putting the torque wrench on it.

2: Perfect way, fabricate a “crows foot” type box wrench so you can use the torque wrench and the screwdriver simultaneously. In doing so there is a leverage factor that needs to be computed to arrive at a different (lower) torque spec and you probably need four hands to do it.

3: My way again. Put a nut and bolt together in a vice and torque to the spec, put the undoubtedly shorter box wrench on it to get a feel for how tight that is. Repeat a few times and feel how tight that torque feels. Then set the torque wrench aside and do it by hand.

Now that we are done lets just double check our work, remove the bar from the rear wheel and rotate the engine forward to the checking points, hold it there with the rear brake momentarily and confirm a small amount of lash.

Re-assemble don’t forget, add coolant, return the toothbrush to its owner, go ride.

Titanium Valve Supplement: Ti is used in the 450SX, 450SMR, 525 SMR.

Ti adds an issue we don’t have with the steel valve models. Ti makes a good valve for some time, you get a fairly steady valve adjustment for some time, then one day the clearance starts changing rapidly, shortly the head falls off the valve and the damage can be huge!

The way we can mitigate this is to monitor the adjustments needed to keep within spec, when the cumulative changes to those adjustments on any one valve reach a number somewhere in the .005” to .0075” area there is an explosion approaching, a wise rider would park it and replace the valves rather than flog it until it blows.

What I want you to do is keep records of your changes. The following is in part credited to Caflash: Make scratch lines with an awl on the lip of the opening for the valve covers in line with the slot in the valve adjuster. Each time you readjust make new mark maybe double fine lines next to each other for the second 3 lines for the third. With this and knowing how much distance is in a full turn then you can see the wear on the valves over the long run. One full turn is .030” so ¼ turn is .0075 so that is about as far from the initial setting you should go with Ti.

This is a bit like a Top Fuel Drag car throwing away a $3,000 crankshaft at 12 runs because at 15 they are at high risk of breakage and likely to do $50,000 in damage not to mention danger. In our case its more like $400 set of valves and $2,500 damage & pushing out of the woods. Still running a Ti valve that has stretched to a point approaching failure is not cost effective!

  • Like 1

Share this post

Link to post
Share on other sites

Gear ratio changes; Often we want to modify our bikes intended use, nothing can make a dirt bike feel out of sorts with our use more then gear ratios not suited to our style.

RFS models; 2000 and up 400, 520,525, 450EXC/MXC/XC 2003 up, SX 2003-2006 and 250EXC 2002-2006*. Most common conversion is to take a 4 speed SX model and change to a 6 speed, on the RFS engine bikes;

Note 1: All 4th gears are the same

Note 2: There are two sets of ratios for all gears except 4th, of the 400 & bigger RFS models

EXC’s use Wide Ratio (WR) 6 speed.

MXC’s use Close Ratio (CR) 6 speed

SMR’s use Close Ratio (CR) 6 speed

400SX use Close Ratio (CR) 6 speed

525XC use Close Ratio (CR) 6 speed

450XC use a Hybrid, being WR for 1st & 2nd, then CR for 3rd – 6th

450SX 03-06, use Close Ratio 4 speed

520 SX use Close Ratio 4 speed

525 SX use Close Ratio 4 speed

Note 3: to change those 4 speed models to 6th, you are adding 5th & 6th ratios. Now this gets complex, from here on when I speak of a “ratio” it is made from a mating of two “gears”. When I speak of a “gear” I mean just one of those two “gears”! The 6 speed is a complex design where some gears serve two duties, a; drive another gear too make a “ratio” and b; slide over to engage a different gear. Thank Rubin Helmin of Husqvarna for developing this in 1972 (it came to KTM via the Huseberg acquisition in the late ‘90’s). Without this design a 6 speed would be about an inch wider then the space between your feet. Do to this some gears perform two functions 2 of the 4 gears that it takes to make up the 5th & 6th ratios are already in your 4 speed! IF you use those 2 gears in your 6 speed conversion you must buy mating WR gears!!!

Plan 1: is add 2 gears, gain 2 ratios, each “wide”. This works nice for the guy that wants to keep the bike “racy” with the close ratio 1-4, then use tall 5th & 6th for road sections, generally with this combo you will run low final drive such as 13x52 to get first “trailable”.

Plan 2: is buy 4 & toss 2 gears, to get all CR, will make the bike more racy, less do it all

Note 4: When doing this conversion there is a pin in the shift drum that blocks if from turning past 4th, if you fail to remove the pin you will only be able to select 1-4! That will ruin your day.

*This and 250EXC 2002-2006 while the same basic engine little in the trans interchanges with the other RFS models.

  • Like 1

Share this post

Link to post
Share on other sites

Deceleration Pooping/Hanging Idle

Popping: I frequently hear someone say “I have popping in the exhaust under deceleration so my carb must be lean!” Deceleration popping tells us a couple things;

1: Inside the exhaust pipe is hot.

2: Idle circuit is allowing fuel into the engine.

3: Somewhere the fuel in the exhaust pipe (which is not burnt as we are not allowing oxygen into the engine) is coming into a source of oxygen! Thus finding some air so it can explode!

That’s it! It does not mean its lean! You can richen up the idle mixture until the exhaust is no longer hot and the popping may go away? But now you have a cooler combustion chamber and the AC pump is going to have more trouble getting the engine to respond to the twist, you may find yourself going around in circles?

If you want to understand the engines function better? The engine is a big air pump, as long as the engine is turning over it is trying to draw air in. That airflow is blocked by the throttle slide so under deceleration there is very high vacuum on the front side of the slide.

What is happening is a combo of two things:

1: High vacuum at the intake port is sucking fuel from the idle circuit, that tiny orifice forward of the slide so some fresh fuel is being run thru the engine, as the air supply is almost closed off this fuel goes thru the engine mostly unburned. (BTW, several years ago when cars got FI and the mileage improved! The reason the mileage improved is the FI shuts off the fuel when the vehicle is driving the engine).

2: Under deceleration high vacuum as the exhaust valve opens before BDC at the end of the power stroke it draws air from the exhaust back into the engine. The exhaust had momentum going out, suddenly there is suction making it reverse. At that moment the suction at the exhaust valve area is so high that the tinniest leak at the head pipe will draw in fresh, dirty air!

“Fresh” in that it has lots of Oxygen! This ignites the un-burnt fuel out in the exhaust port!

Dirty in that it brings with it dirt that is around the front of the cylinder head, this gets under the valves and causes some minor pitting of the valve. Not catastrophic but when I take a head apart I have a pretty good idea of how good your head pipe seal is! (it has been a growing problem since the Siamesed pipe design that KTM went to in 04).

Dave’s way;

1: Do not use popping as a gauge to lead you to modifying your jets,

2: Remove the pipe, seal its inside with high temp silicone, let it dry a few days before you start the engine.

BTW If you just bought a pipe that says “Big” on it, sorry I can not help.

Hanging Idle

Related to the carb but worth covering here is “Engine does not return to idle properly!” It is almost always some combo of;

A: Throttle cables have too little slack in them so they are binding in the bottom of the pulley grooves! (very common, they need more slack then you expect).

B: O ring is missing off the idle mixture screw. (common if someone has been tampering with it).

C: The vacuum release plate which is on the engine side of the Throttle Slide in upside down. They have been know to come that way, if in question remove the carb and look in from the engine side, if its correct you should see a 1/4" hole near the bottom. If its not visible that plate is inverted and the hole is out of site at the top. without the hole the slide will snap shut with engine off but when running air gets caught between that and the slide and the slide drops almost to idle, then hangs there for a second. Other then correcting one installed wrong there is no reason to ever remove the slide! The factory seals the screw that holds it with paint for a reason, do not tamper!

D: Idle mixture is very very lean!!! (Not common).

E: Air leak forward of the carb, very rare on the RFS.

About the author

Dave Hopkins is a former Husky dealer, former off road competitor and mechanic, today sells Real Estate in the Seattle area and as a hobby business does head work on MC cylinder head primarily KTM & Husky. Can be reached at davehopkins@windermere.com

  • Like 1

Share this post

Link to post
Share on other sites

RFS Clutch Packs

2002/2003 Clutch Basket 59032000276 76-T/20-T 2001

inner hub 59032002200 RACING '03

Intermediate Disk 1 mm 59032010100 1MM 2002

Lining disk 1.8 mm 59032011000 1,8MM

Intermediate Disk 1 mm 59032010100 1MM 2002

Lining disk 1.8 mm 59032011000 1,8MM

Intermediate Disk 1.4 mm 59032010200 1,4MM 2002

Lining disk 1.8 mm 59032011000 1,8MM

Intermediate Disk 1.4 mm 59032010200 1,4MM 2002

Lining disk 1.8 mm 59032011000 1,8MM

Intermediate Disk 1.4 mm 59032010200 1,4MM 2002

Lining disk 1.8 mm 59032011000 1,8MM

Intermediate Disk 1.4 mm 59032010200 1,4MM 2002

Lining disk 1.8 mm 59032011000 1,8MM

Intermediate Disk 1 mm 59032010100 1MM 2002

Lining disk 1.8 mm 59032011000 1,8MM

Intermediate Disk 1 mm 59032010100 1MM 2002

Pressure Cap 59032003100 2003

pack total 22.2 mm

2004 Clutch Basket 59032000276 76-T/20-T 2001

inner hub 59032002200 RACING '03

Intermediate Disk 1 mm 59032010100 1MM 2002

Lining disk 2 mm 59032011100 2MM 04

Intermediate Disk 1 mm 59032010100 1MM 2002

Lining disk 2 mm 59032011100 2MM 04

Intermediate Disk 1.4 mm 59032010200 1,4MM 2002

Lining disk 2 mm 59032011100 2MM 04

Intermediate Disk 1.4 mm 59032010200 1,4MM 2002

Lining disk 2 mm 59032011100 2MM 04

Intermediate Disk 1.4 mm 59032010200 1,4MM 2002

Lining disk 2 mm 59032011100 2MM 04

Intermediate Disk 1.4 mm 59032010200 1,4MM 2002

Lining disk 2 mm 59032011100 2MM 04

Intermediate Disk 1 mm 59032010100 1MM 2002

Lining disk 2 mm 59032011100 2MM 04

Intermediate Disk 1 mm 59032010100 1MM 2002

Pressure Cap 59032003200 2004

pack total 23.6 mm

2005 Clutch Basket 59032000276 76-T/20-T 2001

inner hub 59032002200 RACING '03

Intermediate Disk 1 mm 59032010100 1MM 2002

Lining disk 2 mm 59032011100 2MM 04

Intermediate Disk 1 mm 59032010100 1MM 2002

Lining disk 2 mm 59032011100 2MM 04

Intermediate Disk 1 mm 59032010100 1MM 2002

Lining disk 2 mm 59032011100 2MM 04

Intermediate Disk 1 mm 59032010100 1MM 2002

Lining disk 2 mm 59032011100 2MM 04

Intermediate Disk 1 mm 59032010100 1MM 2002

Lining disk 2 mm 59032011100 2MM 04

Intermediate Disk 1 mm 59032010100 1MM 2002

Lining disk 2 mm 59032011100 2MM 04

Intermediate Disk 1 mm 59032010100 1MM 2002

Lining disk 2 mm 59032011100 2MM 04

Intermediate Disk 1 mm 59032010100 1MM 2002

Pressure Cap 59032003300 W. OIL PASSAGE 05

pack total 22 mm

2006-2007 Clutch Basket 59032000476 76-Z/20-Z 01

inner hub 59032002250 2006

Intermediate Disk 1 mm 59032010100 1MM 2002

Lining disk 2 mm 59032011100 2MM 04

Intermediate Disk 1 mm 59032010100 1MM 2002

Lining disk 2 mm 59032011100 2MM 04

Intermediate Disk 1.4 mm 59032010200 1,4MM 2002

Lining disk 2 mm 59032011100 2MM 04

Intermediate Disk 1.4 mm 59032010200 1,4MM 2002

Lining disk 2 mm 59032011100 2MM 04

Intermediate Disk 1.4 mm 59032010200 1,4MM 2002

Lining disk 2 mm 59032011100 2MM 04

Intermediate Disk 1.4 mm 59032010200 1,4MM 2002

Lining disk 2 mm 59032011100 2MM 04

Intermediate Disk 1 mm 59032010100 1MM 2002

Lining disk 2 mm 59032011100 2MM 04

Intermediate Disk 1 mm 59032010100 1MM 2002

Pressure Cap 59032003350 WITH OIL BORE 06

pack total 23.6 mm

Share this post

Link to post
Share on other sites

Part numbers:

Honda accelerator pump diaphragm. 16021-MEB-771

RFS cooling fan. 59035041044

RFS rear wheel bearings, all. 6005 2RS

RFS front wheel bearings 03 on. 6906 2RS

RFS front wheel bearings 00-02. 6904 2RS

RFS brake pedal bearings (2) 608 2RS (common inline skate bearings)

RFS spark plug 00-02. NGK CR8EK Gap=0.6mm = .024 inch.

RFS spark plug 03 on. NGK DCPR8E Gap=0.6mm = .024 inch.

250 SXF spark plug. NGK CR9EBK

RFS heavy duty battery. YTZ7S...the 04 needs the 05 battery box. Part 59011055100

Radiator fan switch. BMW 318i, use 91C which is 195 degree versus the 180 degree that KTM uses. Saves your battery.

  • Like 1

Share this post

Link to post
Share on other sites

Jetting overview, KTM RFS with Keihin FCR carb---Dave Hopkins

1: Before we consider modifying jetting on a used bike it needs to be in good shape, DO NOT try to take an engine that is down on compression (which will usually act similar to one that is rich) and re-jet it to correct for the condition. Do a simple compression test first, rough rule of thumb, if its below 115lbs it can not be tuned.

2: Just because you bought a pipe with a decal does not mean it needs to be re-jetted

3: If you bought some accelerator pump cover that is supposed to revolutionize the world, send it back, it is not needed.

4: Do not tune the carb by “Deceleration Popping”.

Please read “Carb Setup 101” and “AC Pump 101” for better understanding of the systems

5: Keihin needles are available in several series of tapers. These are designated by the 3rd from last letter, the two Kehein tapers we use are “E” which is very steep, and “D” which is very shallow. Warning, the “D” series has so little taper that it blocks the flow on the main jet. Because of this on certain models the main jet is meaning less.

Just a rough range of where you should be:

02 250EXC/RFS: These needed a 48 pilot, and as the stock needle is too lean work best with either;

JD kit, or

OBEVP needle, main jet about 175

A good aid on these is the Honda diaphragm (see ac pump 101)

00-02 400: These needed a 48 pilot, and as the stock needle is too lean work best with either;

JD kit, or

OBEVP needle, main jet about 155

A good aid on these is the Honda diaphragm (see ac pump 101)

As a side note. HT Racing has a smaller tube header pipe that makes the bog on the early 400 much easier to tune out....Bill

00-02 520: These needed a 48 pilot, and as the stock needle is too lean work best with either;

JD kit, or

OBDVP needle, main jet about 175

A good aid on these is the Honda diaphragm (see ac pump 101)

03-06 250EXC/RFS: These needed a 42 or 45 pilot, and as the stock needle is too lean work best with either;

JD kit, or

OBEVP needle, main jet about 175

A good aid on these is 03-05 models you can do the BK Mod or any year the Honda diaphragm and can be made a bit more responsive with an Oring on the throttle linkage (see ac pump 101)

03-06 400: These needed a 42 or 45 pilot, and as the stock needle is too lean work best with either;

JD kit, or

OBEVP needle, main jet about 155

A good aid on these is 03-05 models you can do the BK Mod or any year the Honda diaphragm and can be made a bit more responsive with an Oring on the throttle linkage (see ac pump 101)

03-07 450/525 EXC*/MXC/XC/XCW: These needed a 42 or 45 pilot, as the stock needle is too lean work best with either;

JD kit, or

OBDVP needle, main jet about 175

*07EXC to run right must have a Canisterectomy or a Stealth Canister disablement!!!

A good aid on these is 03-05 models you can do the BK Mod or any year the Honda diaphragm and can be made a bit more responsive with an Oring on the throttle linkage (see ac pump 101)

03-06 450/525 SX/SMR: These needed a 42 or 45 pilot, here the stock needle becomes more tolerable as with the bigger carb the needle is lifted further, thus wide open if further down the taper, thus stock is workable, some say they have more power with the JD kit

A good aid on these is 03-05 models you can do the BK Mod or any year the Honda diaphragm and can be made a bit more responsive with an Oring on the throttle linkage (see ac pump 101)

06 250 SXF

Stock is fine, let it break in, make certain compression is up there, a ring only last 40 hours and trying to re-jet when your down on compression is not productive. As always the JD kit works excellent but I fail to be convinced it is warranted here, stock (once broken in and the AC pump limited) is pretty darn good.

A good aid on these is the Honda diaphragm and can be made a bit more responsive with an Oring on the throttle linkage (see ac pump 101)

07 250 SXF/XCF

Stock is fine, let it break in, make certain compression is up there, a ring only last 40 hours and trying to re-jet when your down on compression is not productive. As always the JD kit works excellent but I fail to be convinced it is warranted here, stock (once broken in and the AC pump limited) is pretty darn good.

This is different from the 06 in that it has a “Leak Jet”. I would plug the leak jet and restrict the travel of the AC pump instead with the Honda diaphragm and can be made a bit more responsive with an Oring on the throttle linkage (see ac pump 101)

07 250XCF-W

Get the needle for the SXF/XCF and refer to the notes above, stock needle is useless.

07 450/510SXF

In colder climates/winter they like a 42 pilot jet, the rest of the jetting should be workable. A good aid on these is the Honda diaphragm and can be made a bit more responsive with an Oring on the throttle linkage (see ac pump 101)

Rule of thumb, Pilot effects starting

First stage of needle effects idle thru ¼ throttle, if this area is not happy nobody is happy!

Needle taper effects ¼ thru ¾ AND on a “D” series needle beyond ¾, small engines need more taper then bigger ones!

Main effect only wide open

Other mods

I frequently modify carbs to suit the customers needs;

Cold weather riders I enlarge the starting jet, its still works in warm weather, you just need to take it off choke more quickly

Big motors, 525 & larger I modify the needle to fit the application as I am not satisfied with that is available.

And 450 & larger I modify

Share this post

Link to post
Share on other sites

An excellent write up from Dave Hopkins. 👍

Chapter 1: KTM Valves


As a matter of economics KTM has opted for a fairly soft grade material for the intake valves. Example their exhausts valves (which are fine) sell for about $40 and the intakes for about $22. As a test, Stainless Steel is not magnetic, an alloy of “Steel” and Stainless Steel” however is magnetic. The KTM intake valve is magnetic, the KTM exhaust like the Kibblewhite replacement valves I use are non-magnetic.

The result is their intake valve is too soft to be compatible with the hard seats and the intake literally forms to fit the seat becoming what is known as “cupped”. When the valve loses its shapes the valve adjustment is constantly changing, intakes clearance closing up. To deal with this KTM cuts the seats 45 degree face undersize to allow a thicker part of the valve head to beat on the contact area to keep the soft valve alive for a while. If you took a new valve & head and applied blue die to the valve and lapped it with fine lapping compound so you can see the contact area this leaves a contact area on the valve about 1.5mm smaller in diameter than the proper contact area which is nearer the valves edge. If a machinist where to cut the seat out to fit the valve proper as they are cutting on a 45 degree angle the valve is going down the same amount the contact area is going down about 1.5mm. This results in a nice valve job but the valve is so buried into the port that the combustion chamber volume is increased by the valve location, the compression ratio is compromised and often you are out of adjustment on the valve before you start!


A proper seat contacts the valve almost at its outer edge, a contact further in is like having a smaller valve, the area that can flow is reduced from its potential. The stock KTM seat has a 17° top cut, 45° face that is way down on the inner edge of the valve, then drops sharply to a approx 75° angle to the base of the seat where it becomes 90°.

What happens from here, a technician that knows seat work would want to move the seat out on the valve near its edge, it needs to move about .050” measuring on the radius. To do so the valve would also go down about ¾ of that amount (the amount it goes down is less than 1 to 1 do to the fact you working against the 17° top cut) so it really goes down about .040”. Problem is now our valve is sunk, compression ratio is lost and we are nearly out of adjustment

Kibblewhite, a custom valve manufacturer, first has a better grade of material, second they make a valve 1mm oversize so I can make the seat right, hold the valve “up” into the combustion chamber and keep the compression ratio up. To make this work out right we also had to alter the stem length slightly to keep the stem length correct for valve adjustment and correct spring tension. In doing this we recapture what otherwise would works out to a .6 to 1 loss (example 11 to 1 could drop to range of 10 to 1 to 10.4 to 1) in compression ratio. Maintaining what has been lost from sunk valves yields a significant restoration in torque!

So when I am done we have a better valve, a proper fit in the combustion chamber, proper stem length and the meat within the seat to make the seat the way they are supposed to be and we have what some would call a 5 angle valve job;

1: 17° top cut is still there, now slightly narrower,

2: 30° cut, very small, there to take off the sharp edges which hinder flow,

3: 45° face that is now centered on the face of the valve (much closer to the edge),

4: 60° cut on the bottom side is used to narrow & size the seat contact area to its desired width, and

5: From there all the way down to the port is hand blended.

On the intake side I attempt to maintain a large bowl under the seat, and

on the exhaust as the air is flowing the other way I try to retain a slight radius below the seat to help guide the flow to the port.

Cost for reconditioning a typical head with these valves is under $300.

RE 450SX

First you need to analyze what you do with the bike? A highly competitive MX racer has the problem that in the rush to the first turn he can not hear the engine and is very apt to miss shift points. The resulting over rev is where Ti valves are needed, for all other general off road riding the same valves I use in the XC line are more appropriate.

For stainless conversion, most but not all 450SX have a spring that is suitable but as they are not all the same I can not confirm this until I have it here.

For Ti there are a few options;

1: In 03 when KTM first switched to Ti they got stuck with a bad batch which was only the first part of the 03 production. As the early valve had a very short fuse most of those bikes have been retrofitted

2: Late 03 thru current production Ti has been quite good. The pricing is way up there, $160ish last time I bought some. Is my preference not to log a lot of hours on them as when they die they destroy the engine!

3: There are a couple aftermarket companies that make a “billet Ti”. I consider these to be a special order, too expensive to stock. $500+ for a set, wana bump elbows with RC & Bubba, we need to talk, wana go trail riding, play on a track some, forget Ti, lets do a stainless conversion.

Another issue with Ti. With Stainless valves the KTM Bronze Guides are as good as it gets. Unless coated, Ti stems do not get along with Bronze. The Ti valves have some sort of coating but it is not satisfactory so from the first Ti in 03 450SX thru 05 the rate of guide wear has been very high. For 06 KTM changed the guides in an attempt to cure this. If you have many miles on the Ti your guides will have some wear, seldom re-useable.

One other 450SX issue, as the factory machined the crank smaller to save weight the bolt used to index the crank at TDC is too short. It is very common to miss TDC and thus miss time the cam on this engine! Remind me when I ship it back and I will send you a longer TDC bolt!

RE 525SX

This being a bit lower RPM engine has the same valves as the XC line, for some reason they have a goofy valve spring that I usually toss.

RE 525 SMR

Prior to 06 these have had some serous issues with guide wear. The head/valves/springs are the same as the 450SX but the RPM they are subjected to is much higher. Don’t be surprised when I tell you the guides are wasted!


When springs are needed I can get a superior spring from Kibblewhite that has a Ti retainer for only a few dollars over the cost of the KTM EXC spring. (EXC is well over $110, KW is about $138).

CHAPTER 2: Performance work:


On the RFS engine the intake ports in this engine are generally considered to be too big. Thus “Porting” is not so much “more, bigger, better” but a little reshaping and smoothing, blending the port to the seat and then adding a polish job offers an improvement over stock.


As a result of design compromises from using one head on several sizes of engine, the valves are quite close to the side of the combustion chamber, I like to run a radius cutter around the outside of the seat and open this area up a bit. How far I cut this out varies with the application and how many CC’s of volume we dare sacrifice and retain compression ratio.

Combustion chamber diameter;

As the combustion chamber is sized for the 89mm bore. On the 95mm & bigger engines I will blend the lower edge of the chamber below the intake valves out to more closely match the bore.

To help you understand compression ratios, lets say we have a combined volume in the head, head gasket and valve relief’s in the piston of 47cc with the 89mm head gasket or 49 with the 95mm gasket, then:

Example: note these numbers are estimated and include cylinder head of 40CC, head gasket, deck clearance and valve notches.

400 400 + 44* = 444 ÷ 44 = 10.0 to 1

450 EXC 450 + 47 = 497 ÷ 47 = 10.6 to 1

450 SX 450 + 43** = 493 ÷ 43* = 11.5 to 1

520/525 510 + 49 = 559 ÷ 49 = 11.4 to 1

*has a dome of approx 3cc

**has a dome of approx 6cc

As you can see as the engine gets bigger the compression ratio goes up with the same head! Do to this I remove less material when unshrouding the valves on the smaller engines.

I recently measured the cylinder head volume at various stages;

A stock valve/combustion chamber has the intake valve when open about 3mm for ¼ of the circumference of the valve is only 1.25mm away from the side of the chamber and exhaust is about 2mm, thus flow is impaired, opening the valve is doing almost nothing for ¼ of the circumference of the valve. On a compression ratio sensitive application unshrouding I set the radius cutter so that there is 2.5mm clearance around the valve. This allows for a healthy flow and only a 1CC increase in volume (approx a 2/10 point loss in compression ratio). On a big inch domed piston job I set the cutter slightly larger.

New stock was 39CC

Stock with some use, intake valves receded into the head 40CC

Stock with lots of use, intake valves receded into the head 41CC

With my oversize Kibblewhite valves 37.5CC

With my “un-shrouded” chamber at 3mm valve clearance 38.5CC

With my “un-shrouded” chamber at .3.5mm valve clearance 39.5CC

(there will be minor variations from these numbers)

400: On 400’s the compression ratio is too low to start with so it is vital to maintain every cc of material in the combustion chamber available, so I set the valves as high as possible in the combustion chamber and leave the chamber alone to maintain all possible volume!

450EXC/MXC: On these 89mm bore application the compression ratio is a little less critical, a very light unshrouding of the valve is my preference setting that valve to combustion chamber clearance of around 2.5MM and polish the combustion chamber.

450XC: On this 95mm bore application I do it the same as the 450EXC except at the lower edge of the valve pocket I blend the chamber out to slightly towards matching the 95mm bore size.

450SX: On this 95mm bore, hi compression piston application I do it the same as the 450XC except at the lower edge of the valve pocket I blend the chamber out to more closely match the 95mm bore size.

525: On the 525’s mathematically the compression ratio is less of an issue so even though the piston is flat top we can treat the head the same as the 450SX.

525-560 and High compression piston combos: As the compression ratio is less of an issue my preference is to un-shroud the valves to about 3.0mm clearance and open up the combustion chamber to blend to more closely match the bore.

SXF This is almost identical to the Husky head and I do a few of those, as stem length, valve location in relationship to the cam is much more critical the labor/pricing is a bit more, in time I anticipate I will be having custom stainless steel valves made for them as well. On these engines you need to send me all of your cam, finger follower, shims etc. and labor rate is $20 extra to cover setting the stem length.

Chapter 3: Parts and service items;

Cam chains: I hear a lot of talk about cam chain wear, so far I am not convinced that counting ‘clicks” on the chain tensioner means anything. The proper test is to lay the chain out flat on the bench, count out ten rollers, then with a dial or digital caliper measure the inside to inside dimension. It should not exceed _______”. If you want to send your chain with the other parts I can make this measurement for you.

Cam bearings

I recommend changing the cam bearings every year or every time the engine is open, if you want to send the cam I can pull the old ones off and press the new ones on.


I usually have “top end” gasket sets in stock.

Valve seals;

Typically in stock

Rings, if there is any question remove the top ring and ship it and the cylinder with the head so I can check the “end gap” for you.

6x55 bolts, there are two bolts on the right side, top of the cam box cover just for & aft of the spark plug that locate the rocker shafts. The rocker shaft works against the bolts and makes a notch in them, the bolt is under additional tension when the engine heats up and these break at the notch. There are two cures;

1: de-burr the holes in the rocker shaft, you can send those shafts with the head if you want me to do so.

2: replace the bolts with extra hard “Allen head” bolts.

I have those bolts in stock, under a buck a piece

Chapter 4: Updates

00 bikes should have the water pump impeller changed to a newer one

00-01 bikes should have the cam bearings replaced

00-02 bikes should have the cam sprocket replaced with 03 or newer

00-02 bikes should have the lower cam chain guide replaced with 03 or newer

03-05 450 SX usually need valve guides

All 525SX should have valve springs upgraded.

Any should have the two 6 x 55mm bolts on the cam cover that locate the rocker shaft upgraded to hardened bolts!

Chapter 5: Carburetors;

A carb service includes

Identify the model & use of the bike and try to tailor it to suit the riders needs,

Each carb is given an ID # for future reference,

check the vacuum release plate,

set the slide height,

I drill the spray nozzle for the AC pump oversize for most applications (has a similar effect as the O-ring mod without adding the pressure on the rider’s arm the O-ring does).

Check, test/clean the check valves for the AC pump

Check/adjust the starting point of the AC pump

Check/adjust/modify as needed the duration of the AC pump

Check the idle mixture screws tip, O-ring, washer & spring, set at estimated setting

Check float level

Note jets, make recommendations as seen fit

Re-route and tag the vent hoses.

This service is $100, Owner needs to acknowledge that I can not run and test their bike but the setup will be as close as I can make it at the shop! Actual jetting in 99% of the cases will be close enough to enjoy the next ride but perfection may require some additional tinkering.


Remove seat, tank, exhaust, carburetor, radiators & hoses.

Remove the left of those bolts that hold the rubber piece the gas tank slides onto.

Remove the top Banjo bolt from the head oil line, be careful not to loose two copper washers.

Remove the 6 bolts holding on the 2 valve covers, be careful not to loose any copper washers, typically the center bolt on each cover should have a washer (those bolts go thru to oil which wicks up the threads).

Remove the 6? Bolts that hold the top cam cover on, note the middle one will not come out, also note there are several lengths of bolts, you may want to lay these in some order?

Remove the water pump cover, remove a snap ring, then with two screw drivers slide the impeller off, be careful not to loose the drive pin behind it. If you break the impeller, the good news is its very inexpensive.

With a punch tap up on the inside of the top of the water pump, the cam box cover should come loose, if it does not recheck for a missed bolt, then tap again. Once it is broken loose you should be able to lift it up, hold up that center bolt, tilt the cover up on the left and rotate about 1/8 turn counter clockwise to get it out.

Locating TDC: I have had too many customers (and myself once) assemble the engine with the TDC lock down bolt in, piston at the top and think that they are at TDC but been tricked by a notch in the crank that is not TDC! 450SX, 525 SX & SMR are double prone to trick you!!

1: Remove the magneto cover, with a 17mm wrench (not a ratchet) roll the crank counter clockwise until the cam lobes are down at 5 & 7 O’clock!

2: Note on the flywheel there is a small block of steel (steel block) welded to the outside. Also note about 2 O’clock a black box, KTM calls the “Pulse Coil”. Top Dead Center (TCD) is when the right/clockwise edge of the steel block matches the left/counterclockwise edge of the Pulse Coil.

3: On the bottom front of the engine case a bit right of center there is an 8mm allen head bolt. This needs to be removed, the thick washer it has needs to be set aside, On 400-450-525 EXC/MXC you can screw the bolt in and it should go into a notch in the crank. 250, 450SX maybe 525SX, defiantly 525SMR this bolt is often too short! If so the crank can rock forward and back slightly even with the bolt in place. If so get a longer bolt and grind it to a point so the crank can be properly secured!

This bolt should go into a notch in the crank, when in;

a) the steel block and pulse coil should alien as above, and

👍 the cam lobes should be down, 5 & 7 O’clock

c) now look at the cam sprocket, at the inner edge of the chain there should be a punch mark matching each gasket surface of the top of the head.

Will the crank move fore & aft? If so try to tighten the bolt, if the crank can still be moved we need a longer bolt!! If so tell me when you send the head! I would much rather make you a bolt then have you have a crisis on assembly!

Remove the center bolt from the chain tensioner and the spring that comes out with it and set aside. Next remove the outer two bolts, slide the tensioner off, then holding it upright (same orientation as when installed) grip the center plunger in the middle and pull it outward while watching the little ratchet that runs on the top of the plunger. If it clicks two or more times you’re good to go, less than 2 you’re close to ready for a chain. Then try to push the plunger back in. If it can be slid in and out with out clicking your tensioner is shot.

Then remove the cam chain tensioner,

First I would have the cam in the position that the lobes are at 5 & 7 O’clock, piston at TDC, and the crank locked down.

Next if the engine is not completely coming apart stuff rags around the chain & sprocket are to prevent dropping stuff inside.

Next take two tie wraps and go thru the holes in the cam sprocket and around the chain at 11 & 1 O’clock so the chain does not flop & fall when you "break it".

Then working on the top center of the upper sprocket we must break the chain, picking a link straight up is easiest, there are two ways:

1: Without the KTM Chain Tool. Use a small grinder such as a Dremel tool and grind down the pins on a pair of the tips of one chain link, tap them out the back. OR

2: With the KTM Chain Tool:

The center screw of the tool needs to be backed out so that tip is retracted.

The Anvil is set aside, not used for disassembly

The hole in the outer threaded part is going to go over a rivet.

The C clamp like part goes around the chain, the machined "notch" on the back goes around the chain pins on the back side

The outer threaded piece needs to snug down against the chain

Then the inner threaded portion is tightened and it pushes the pin all the way thru, have a small magnet in hand to catch it.

Next loosen the center part an inch or so, loosen the outer part way out so the centrer pin is retracted again, then the entire "C" clamp moves to the next pin of the same link plate, repeat, again catch the pin with the magnet.

Now then this is where we get in trouble, when you loosen the outer (big) thread both side plates are going try and fall into the engine! Two magnets and three plus hands is recommended. Also recommend you inventory the link pins & plates as it comes apart, when you confirm two pins & two side plates, toss them!

Remove 3 small bolts (front, left & rear) that hold the cylinder to the head, (the rear one is a pain)

Remove 4 head bolts, with a couple of taps of a mallet it should break the seal of the head gasket and easily lift off.

For head service ship to

Dave Hopkins

11411 NE 124 Street, Suite 110

Kirkland, WA. 98034


450SX! 450SMR! 525SX? 525SMR? Let me know if you need a longer lock down bolt to get full engagement on the crank!

Send the head with,

cam if you want me to change the cam bearings and

carb if you wish it to be serviced/modified.

When shipping please drain gas, put carb, head etc in Zip Lock bags, then pack properly for protection.


Crank is still locked down at TDC?

Look at the piston and confirm that it is at the top!!!!!!!!!!!!!!!!!!!! Some cranks have another notch or hole that the TDC bolt can go into so some get tricked into a false TDC and 450SX & 525SMR have too short of a TDC bolt! An error here can lead to valves hitting the piston! Double check at the flywheel & pulse coil as I explained in Chapter 6.

De-carbon the top of the piston taking care to clean out the valve pockets.

Make certain all old gasket material is removed from the top of the cylinder, water pump cover etc.

Put the head gasket in place note there should be a tubular dowel over the front & rear small bolts! If either is missing from the cylinder, is it stuck in the head? If so that’s fine we just don’t want to loose it. Make certain the gasket is over that dowel AND confirm that no portion of the gasket is hanging inside of the bore! (89mm head gasket on 95mm bore makes a nasty knock!) 97mm big bore kits etc, same problem so pay attention!

Optional; once we are confirmed that we have the correct head gasket, remove the gasket and spray it with Silver paint. This helps the new gasket seal.

Press the head gasket in position, note there are two hollow dowels in either the head or the cylinder to align the gasket.

Set the head on.

Put Anti Seize compound on the threads and under the washers of the head bolts and drop them in place, screw them down until they just contact, work around in a crisscross pattern first time until they just touch, second time until snug, the continuing with the crisscross pattern torque first to 20, then 25 then 30, then 30 to 37 foot pounds (40 to 50 NM).

Install the 3 small bolts (front, left & rear) that hold the cylinder to the head, (the rear one is a pain on Estart bikes)

Lay the cam in place in the position so that the lobes are at 5 & 7 O’clock.

Rotate the cam as needed so the punch marks in the cam sprocket match the gasket surface of the top of the head, flop the cam chain up into place,

Double check that the cam sprocket punch marks are in alignment!

Take two tie wraps and go thru the holes in the cam sprocket and around the chain at 11 & 1 O’clock so the chain is secured.

Slide the new master link in from the rear,

Pack some rags around as its easy to drop the side plate.

Now put the outer side plate on and pinch with pliers so it is secure (although probably not totally seated in place.)


Next as that new link is not yet swedged mark that link with fingernail polish or paint.

Remove the two tie wraps

Next lets install the cam chain tensioner! (note, for 00-01 models we will have it back off when we get to water pump seals as the cam has to be lifted slightly so install temporarily) First we need to remove the center bolt, this has a washer, then a long skinny ball point pen like spring. Set those parts aside, on the main body of the tensioner you need to lift up a small ratchet pawl so that you can compress the plunger, push the plunger in, bolt the assembly back on, then with a large nail or small punch poke in the center hole and push the plunger back against the chain firmly, then if this is final assembly re-install the spring & center bolt.

Now lets temporarily reinstall the cam box cover with 4 or more bolts snug,

Run the valve adjusters down until they contact, then back off 1/6 turn, snug the jamb nuts lightly.

Loosen the TDC lock down bolt 2 or 3 turns.

Ignition cover is still off, with a long 17mm wrench (not a ratchet as it will get away from you when the cam followers pass over the nose of the cam lobe) turn the crank ONE REVOLUTION. (Cam turns ½ crank speed so even though we can’t see them the cam lobes are now 11 & 1) stopping at the TDC point identified by the small steel "block" on the flywheel I described in the disassembly section. That is TDC on the Overlap stroke, both valves are open a small amount and a equal amount, such as 1mm!

Now roll the crank fore and aft slightly, maybe a couple inches at the end of the wrench you are turning it with.

IF there is a tight spot you’re a tooth off from the correct timing spot.

IF it stops solid you’re more than a tooth off from the correct timing spot.

When complete turn the crank the other direction one turn to get back to where you where. Note, the cam comes back to the same point every other turn but the link that you need to swedge does not come up at the same spot every turn.

Chapter 9, Riveting the chain:

Next, turn the outer part of the chain tool out so it has an opening about 1¼ ”, turn the inner part in so the pin sticks in a ¼” or so, slide the chain tools Anvil onto the pin so the side that will go against the chain has the piece that is shaped like a chin link go against the chain.

Slip the C clamp like tool over the chain at the link we need to swedge, run the outer screw in so the anvil is pressing against the chain. The only thing the pin in the center is doing at this point is keeping all the parts in alignment.

Tighten the large thread so as to apply some pressure to squeeze the side plate firmly onto the pins, then loosen.

Next Rotate the Anvil so the grooved part is against the chain, again the pin should still be centering the parts.

Tighten the large thread so as to apply considerable pressure to swedge the pins, then loosen. Those swedged pins should look exactly like the other factory swedges!

If you borrowed my chain tool, please please be careful, its $140 and if the anvil is lost or that pin trashed the tool is junk.

When you are done rotate the engine back to where the cam lobes are down at 5 & 7 O’clock and the cam sprockets timing marks match the top of head gasket surface. Lets avoid rotating from here until we have adjusted the valves, put the lock down bolt in if you wish.

Chapter 10, Water pump seal retainer;

Water Pump Seals! Installing the seals into the retainer:

First there are two types of seals, in 04 the old “single lip” seals where upgraded to a “double lip seal”. If you buy new seals today for an early bike you should get the newer seal!

Seals have a “finished side” referring to the smooth, normally outer part to the “dry side” and a “lip” side, the lip being the sharp edge of the rubber that runs on the shaft to the “wet side”! The “lip” always faces the liquid! Most applications have liquid in, finished side out, here the liquid is out and the dry area in, so we have to install the seals backwards. Pressing them in backwards often leads to a seal getting bent, trick here is, using two sockets, a “pushing socket” that is slightly smaller than the seal OD, and a “receiving socket that the seal will fall into:

1. push out the old seals,

2: push in one new seal we will call it seal "A", forwards, not backwards!

3: push that seal "A" on thru to the back and on out, now set it aside, it is now "sized" so it will push in backwards without bending!

4: Push seal "B" in forward, then push it thru to the far side so it is now "backwards" for the far side.

5: Retrieve seal "A" and press it in "backwards" for the front or other side.

We now have the retainer with two seals pressed in, the "lips" are facing out, they are flush on the outside with a space between them.

Installing the seal retainer into the head! There are two kinds of retainers;

Early (00-02); Nothing wrong with this style, the trend is to update to the newer piece in fact I prefer the early one but it must be assembled before the cam box cover goes on!

We have two identical O-rings, the retainer has two grooves and a “lip” between the two grooves. Note that the “Lip” is partly cut away! Give both O-rings a thin coating of Loctite 515 and put them on the two grooves of the retainer!

The cam chain should be hooked up and riveted but the chain tensioner off. If you have the bullet tool install it on the cam, if not give the seals a good coating of grease and holding the seal retainer at a slight angle slide it over the cam. IF you hold it square the seal lips may get mangled by the cams snap ring groove! Once the seals are part way on the cam, past the snap ring groove we need to lift the cam slightly and rotate the retainer so the cut away part of the flange is down at 5 & 7 O’clock so the retainer can go into place against the cam bearing. Once all the way in the lip drops down into the groove in the head. At this point you proceed to complete the cam chain tensioner, the water pump assembly and cam box cover. Note the cam box cover does not use a gasket, KTM specs Loctite 515, Yamabond is fine, in either case apply it to the head, not the cover and spread it very thin, we want to minimize the amount that can ozze in as any excess will end up in you oil screens!

Late 02-07: The groove in the head mentioned in the prior section has a steel washer in it which holds the cam bearing in place. This must be put into place, then the cam box cover and the Note the cam box cover does not use a gasket, KTM specs Loctite 515, Yamabond is fine, in either case apply it to the head, not the cover (its too easy to get the sealant on the chain when sliding the cover in) and spread it very thin, we want to minimize the amount that can ozze in as any excess will end up in you oil screens!

We have two O-rings, the inner one is slightly larger?? We want to give both a thin coating of Loctite 515 and put the inner one into the head up against the washer that is in the head! The outer O-ring we also give a thin coating of 515 and put it into the outermost groove of the retainer. If you have the bullet tool install it on the cam, if not give the seals a good coating of grease and holding the seal retainer at a slight angle slide it over the cam. IF you hold it square the seal lips may get mangled by the snap ring groove on the cam! Slide the retainer on into place. It commonly trys to come back out slightly like there was a small spring pushing it out, what is happening is the O-ring is rolled up and doing the spring thing. Take a pair of needle nose pliers and put the tips into the two small holes in the retainer, then give it a twist, this will relax the tension in the O rings that was pushing the retainer out! Some of the retainers have a dimple on its face that while not critical is typically installed at 12 O’clock. At this point you proceed to complete the water pump assembly.

Chapter 11, finish up;

Adjust the valves;

We are locked down at TDC with cam lobes pointed down?

If so you get to take the short cut!

Loosen the jam nut (10mm box wrench) and very lightly tighten (one at a time) the adjuster till it contacts the valve, note where the screw slot is aimed, turn the jamb nut so a corner of the hex aliens with the slot, make a small scratch in the cover gasket surface in line with the next hex point left (hex being 1/6th turn to the next point). Then turn the slot to that point, then tighten the jamb nut. In doing so often the adjuster will creep tighter slightly and cause the adjuster to tighten up. What you need to do as you tighten the jamb nut is do kind of an isometric exercise where you are holding the adjuster against rotation with equal and opposite force of the rotation of the jamb nut! This may take several practice attempts. As soon as you have tightened the jamb nut just double check that it did not creep, the slot should be aimed at the mark we made 1/6 turn left of the slot when contact was made. Do all four and do not be timid about tightening the jamb nuts!!!

If you are not locked down at TDC with the lobes at 5 & 7 no short cut for you! Go to KTMtalk.com and print out my article.

Reassemble the rest of the stuff, as always when you fill the radiators, fill to the top, loosen the bleed screw that is near the spark plug and wait for coolant to come out, otherwise you have a air pocket in the head. Some models have another one on the top tank of the right radiator. When all the air is out set the coolant level just ¼” above the bottom of the top tank with the bike level.

Finish up, don’t forget to take the TDC lock down bolt out and put its thick washer back on.

Go ride!

Share this post

Link to post
Share on other sites

For your suspension tips and tricks section, would you want a sort of "cut and paste" of the WP open chamber fork components, pictures, and explanations like the one I did on the "other site"?

I can put it up here "in the wild" and then you could move it to what ever or where ever you wanted it.

Well, here it is.................

Feel free to edit it or rearrange it where it makes the most sense to you. I'd just like to help out a bit and give a little back for all the help I've received.

These photos are from a stock '04 48mm RFS fork, and are Representative of most models, with differing shim dimensions.

First, is a picture of the fork seal area:


Next, is a photo of the Base Valve / Compression Holder:


Here are the three bushings referred to in many posts:


Next is a pic of the bottoming cones and the spring guide:


Here is an exploded view of the rebound rod:


This is a closer look at the rebound piston:


Here is a look at the check plate that many convert to a mid-valve assembly, VERY IMPORTANT! The top out spring has a slightly smaller diameter on one end that is trapped between the top of the rebound rod and the bottom of the rebound tap. This difference is small, and if you forced the wrong end over the rod, it would be damaged.


Here is the "infamous" third bushing in stock configuration. Note the damaged components:


Here are the same components in the "reversed" configuration:


I don't remember where I got this one from, or I would credit it, but here are the cartridge internals assembled and exploded:


And from the same un-remembered source...........the fork outers, exploded:


Measuring Float:

If this gap was, say, 1.25mm it would be considered by most to be a mid valve.


If the gap on this example was, say, 2.5mm (and notice the shims are now all the same size) most here would consider this a check plate.


And here's a couple examples of a few other terms bandied about around here;

Single Stage Shim Stack:


Two Stage Shim Stack


And here are the Race Tech Gold Valve and stock KTM pistons, one side for compression flow, one side for refill (three ports each):


Here is a closeup of the basevalve, and a basic flow diagram.


Here's a closeup of the rebound tap and a basic flow diagram.


And a basic flow diagram of the bottoming cone action.


And here's the cone fully bottomed.


Share this post

Link to post
Share on other sites


You are not alone, so that's why this is here.

First, BEFORE you assemble your forks, look at the pictures below, CORRECT and INCORRECT spring guide / hydraulic stop installation from KTMLew. The spring guide MUST be threaded fully down to the bottom of the cartridge rod or you WILL have trouble with your rebound adjuster. The rebound rod MUST be seated properly, or you WILL have trouble with your rebound adjuster.









OK, so here's your problem (we've all been there too, that's why we know the fix).

The rebound knob you see is not the actual adjuster. Below the knob, in a threaded passage through the fork cap, is the adjuster itself. The adjuster is pointed on one end (to engage the rebound rod), threaded around the body (to travel up and down the fork cap as the knob is turned), and has a "+" shape on top of it (to engage the rebound adjuster knob).

The knob is cross drilled, to accept two small ball bearings and a spring. The fork cap has a small groove machined in it for these balls to run in to secure the knob, and to provide the "clicks" you feel when adjusting the rebound. If you pry this knob off (you probably won't need to) be aware of these tiny spring powered balls, you WILL shoot one across the shop..................trust me. The bottom of the adjuster knob also has a "+" shaped extension to mate with the matching "+" shape on the adjuster (is the light bulb starting to come on yet?).

What has happened is that you probably did not have the spring guide screwed down fully, allowing the rebound adjuster to be screwed too far down into the fork cap dis-engaging the two matching "+" shapes.

I've had good luck taking a pair of needle nose pliers and carefully turning the adjuster clockwise until it engaged the knob again, and the knob would begin to turn when you turned the adjuster. At this point, you can use the knob to fully retract the adjuster back into the fork cap (turn the knob counter-clockwise).

If this does not work, it's time to pull the knob. REMEMBER THE TWO SPRING POWERED BALLS! GMP made the excellent suggestion of putting the fork cap in a zip-lock back, poking a small screwdriver through the bag to pry the knob off inside the bag to keep the balls and spring captured (wish I had thought of that the first time). Once the cap is off, insert a small slot screw driver into the cap, and turning counter-clockwise, retract the adjuster. Replace the knob, assemble the forks using the above pictures as a guide.

FIRST, bottom the spring guide on the cartridge rod.

THEN, screw the fork cap down till it bottoms on the cartridge rod.

LASTLY, run the spring guide back UP to "jam-nut" against the fork cap and tighten it.

And your adjustment should be back.

Hope this helps.

Share this post

Link to post
Share on other sites

So your forks act like they are binding, and you don't know why?

We had an interesting discussion trying to diagnose a set of sticking forks a while back, so I thought I might as well post a "worst case" sticking fork trouble shooting guide. This is things to look at AFTER you have done the usual things like checking for proper triple crown torque, making sure the forks are parallel and not binding at the axle on compression, etc. When you get his far, it's probably crash damage that you are looking for (cart wheel the bike down a hill, wad up in the whoops, etc.).

Nothing normal ever goes wrong for me, it always those "boy, I ain't never see that one before" kinda' things for me.

You've checked for alignment, right?

MotoPro KTM Front Fork Alignment PDF

You've checked for proper triple crown pinch torque, right?

Forks seem to slide right into the trees with no binding, right?

Put a wrench / socket on the axle and turned it to make sure there's no bind or wobble, right?

That's all the obvious things, but before I spent money to send them off to someone else................

I'd try:

1. Pull the forks off the bike, and pull the springs. Reassemble the forks and stroke each one through by hand. Do they still feel right, or is the sticking back? (Bent component, bad bushing, swollen fork seal, etc.).

2. Put forks (with out springs still) back in the crowns and torque to spec. Cycle each fork again. Any binding now? (Bad torque wrench [i told you nothing normal ever goes wrong for me], bent / mis-aligned triple crowns, etc).

3. (With out springs still), add the front wheel next, leaving everything "finger tight", and then go through the alignment routine (spin wheel and hit front brake a few times). At this point, you'll probably need help, or maybe a floor jack, but cycle the front end now. Any binding? (Bent axle, bad bearings [one side crushing in in a bind], bent fork lower [there you go with that "ain't never seen that before], etc.).

4. Properly torque front end and repeat above.

By now you should have found something, if not, my hats off to you! You have beaten me hands down in the "most unusual problem" awards............

Share this post

Link to post
Share on other sites

Carb Vent Rerouting

The stock carb float bowl vent routing from KTM is not only slightly overkill, but can cause problems during deep water crossings. The stock carb has a lower bowl vent, and two upper bowl vents. The lower vent goes to the bottom of the swing arm. The two upper bowl vents are on the right and left side of the carb. Each side is split in two. The lower of the two goes to the bottom of the swing arm. The upper of the two goes up and over the top of the carb to the oposite side, and then goes to the bottom of the swing arm (see photo below).


All of these 5 vent tubes are bundled together at the bottom of the swing arm. This allows all 5 tubes to be submerged together, no longer venting the carb to the atmosphere. This stops the flow of gas into the float bowl, starving the engine and causing it to die (usually at just about the worst possible time, literally mid-stream!).

Here's my solution.


I leave the lower vent tube on each side routed in the stock location, leading to the bottom of the swing arm. I re-route the two upper vents to gether with a "T" fitting, and take one extended vent up into the air box. This allows the two upper vents to stay above the water level, allowing the carb to vent to the atmosphere, allowing fuel to flow even if the lower vents are submerged (see photo below).


Additionally, you can pick up a little "extra fuel mileage" at the same time. The bottom bowl vent has a dual function. it will drain the bottom of the float bowl if you open the Allen-headed drain bolt there (if you think you may have some water gathered by the main jet), and it also vents the top of the float bowl internally by an extended brass tube. Over rough ground when the fuel sloshes around in the float bowl, quite a bit of it leaks out. By making a simple loop with the bottom vent you can prevent this fuel loss. If the bike is layed over, all the vents still work properly, helping to keep the bike from flooding still. And if you want to check for water and use the bottom drain it's a simple matter to temporarily pull the hose out of the routing clip and use it normally.

If you look closely at the photo below, you can see the fuel level in the tube closely matches that of the fuel in the float bowl.


Hope this helps some.

  • Like 1

Share this post

Link to post
Share on other sites

The following was a posted reply to help with understanding accelerator pump effects...

Well at least we are getting closer:ride: Now, I do not say that you need that last 2 seconds of squirt. What I say is that, as far as the bog is concerned, those last two seconds don't matter.

What matters is that first micro-second after the slide opens and the vacuum drops. This creates a lean condition and if you don't have the right amount of fuel squirting into the throat of the carb at that moment, the engine bogs and the only way to bring it back to life is to let off the throttle, which brings the vacuum back up and lets things get going again.

I think last two seconds of squirt is just something KTM is doing to mellow out the motor. It may also be a way to compensate for EPA mandated lean stock jetting, or protect the motor when a casual rider opens the throttle in a tall gear and the bike takes 3-4 seconds to spool up. I'm not really positive why KTM decided to go with such a long AC pump squirt, but I'm confident it doesn't affect the off-idle bog one way or the other.

The fuel from the accelerator pump after 1 second and out to 3 seconds may not result in a bog on the first throttle snap, but what about the 2nd, 3rd, and 4th throttle snap. How often you open the throttle and how fast the motor is spinning, along with the available air (as in elevation - or humidity) will all be major factors in whether the bike runs rich. The longer a bike is rich, the colder the motor gets, and eventually it can't burn an under-atomized stream of fuel (like pouring gasoline on a cold fire, nothing happens). However, if the jetting is extra lean and very hot, like an emissions needle, then it will tolerate a longer stream from the pump ---up to a point. This point shortens if you're snapping the throttle open on a stand, riding at high elevation, lugging the motor, evaluating a cold motor in the garage, etc.

There are vendors that promise "NO BOG" with their products, but this isn't realistic for a single product. The jetting needs to be balanced in every area to minimize a bog. None of the bikes with an FCR carb will keep pulling at 2000rpm and full throttle under load, it's a physics problem that Bernoulli's equation explained in the 1700's.

The graphs below will give you some insight into how far apart a stock KTM without leak jet is from adding a diaphragm and adding a leak jet float bowl. These curves are showing volume of fuel, not duration. If you O-ring or wire the linkage, the volume remains nearly the same, but the spray or flow is faster and the period of time shortens. The least fuel from an accelerator pump on a stock bike is that from a CRF450X with the short stroke diaphragm and a #70 leak jet (bottom-right of graph). The most fuel pushed is the top-left of the graph, from the KTM's with no leak jet. Yamaha is nearly always in the middle.

-----The FAQ of interest...

Will a new needle cure an off idle bog??

-Not necessarily, but the needle is a critical part of making sure the air/fuel ratio is near ideal at every throttle position. The pump stops squirting after a brief period, but the needle controls the majority of the fuel continually and needs to be right for the motor to respond at it's best.



Pump diaphrams, with the KTM's on the left, and Honda on the right-


Leak jet in the float bowl-


Pump springs with different preloading, same effect as an O-ring on the linkage-


O-ring modification to linkage-


Setting the timing screw on the linkage-


Share this post

Link to post
Share on other sites

Here is what I ended up using for a turkey baster mod. EKCO turkey baster from Target, heated up the end and pushed in a brass barb adapter. Secured the end where it touches the baster with silicone/hose clamp, and bought a 1" hard plastic chair end at OSH. I then drilled 3 small holes in the top of the chair end for venting, and mounted it up using zip ties. I also bought 1/4 inch tygon tubing from OSH. In my back yard it works great.




  • Like 1

Share this post

Link to post
Share on other sites
This topic is now closed to further replies.
Sign in to follow this  

  • Create New...