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2005 YZ450F Jetting & Tuning

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Hello All!

 

New member, been trolling for a few years from time to time tho.  Quick background, been riding and wrenching since age 13, almost exclusively in dirt, tho I have owned a few street bikes as well.  Even most of the street bikes I've owned I've installed dual sport tires on, as to adventure down dirt back-country roads.  I'm actually a service writer for a local motorcycle shop, but been a few years since I've been in the motocross game.

 

I recently picked up a fairly clean 2005 YZ450F that came into our shop a few weeks ago.  Suspension is all stock, but it has an Athena cylinder kit, which I believe is the big bore kit.  Not sure who the previous owner was, or how they rode, but it seems to be more finicky than most 450s.  Also, the suspension was basically maxed stiff on all the settings (will finish dealing with that once I get back to the track).  Recently, it was taking 3 or more kicks to start when cold, but stalled a lot in the turns on the S track.  And was near impossible to restart when hot, even with the hot start lever.  A local reputable dealership allegedly rebuilt the carb recently, so I'm confident that the carb is clean, but clueless as to what jets are currently installed.  But, when I went to adjust the air screw with the special Motion Pro tool, it seemed like the air screw was stuck, possibly even bottomed out.  So, I installed a MSR thumb screw and started with the factory spec of 1.75 turns out.  Been playing around between 1.25-2.25 turns out.  No matter what, it had a major flat spot at the bottom, and lots of loud popping out of the exhaust.

 

After several days of tinkering and studying up on the FCR carb, came to the conclusion that it was running too lean.  So yesterday I fired up the bike and let it warm, started at 2 turns out and kept turning an 1/8 turn at a time, blipping the throttle until the exhaust stopped popping.  Right at 3 turns out, it stopped pooping, was able to settle the idle down to around 1800 rpms, and throttle response was crisp and smooth.  It also now starts on the 1st kick without choke at about 60 degrees.  Problem now is, after I it cooled down and I went to ride it for a few minutes after work, on cold start she's puffing a little black smoke, tell tale indicator of richness.  I've always been a 2 stroke rider, so the 450 4 stroke is a whole new beast to me.  I do know and have heard that almost all 450s are very temperamental.  I guess my question is, is it normal for the correct HOT tuning of the carb to be rich when cold?  Thanks!

 

Scottie

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You need a new 45 pilot jet

Yes, it wil be rich near the idle when cold.

You need to warm it up with zero throttle for two minutes before riding.

Your carb is old, so you should replace the wear parts: apump diaphragm, needle jet, slide plate seal

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Thanks McKranface!  

 

So, I got a chance to go ride at the track again yesterday.  Bike is definitely running better.  Problem that I'm having now is when the bike gets hot after about 15 minutes of riding.  When going to accelerate out of a corner, the bike hesitates, and sometimes even stalls.  If it actually stalls, it takes forever to restart.  So, definitely something going on in the idle circuit, and likely is the a/p area as you mentioned.  My co-worker was thinking maybe valves, but the bike feels like it still has plenty of compression when kicking over.

 

Like I mentioned in my first post, I'm new to 4 stroke dirt bike.  But, from what I've been reading, it sounds like these FCR carbs have notorious a/p problems.  Was thinking of ordering a Boyesen Quick Shot, but unsure if the QS3 is better because of the air jet tuning screw, or if QS2 is sufficient and good enough with it's improved design and efficiency.  Also, I only want to tear it down once, do you happen to have a parts list for this particular job?  Or better yet, some Tucker or Western part #s?  And one last thing, with the amount of engine work my bike has, would it be worth buying an aftermarket CDI box?  Bike feels like it still has some bark left when the rev limiter is kicking in.  But honestly, this bike has so much power I haven't even gotten out of 3rd gear yet.  Thanks!

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Issues that occur over time are either heat related or fuel starvation related, NOT jetting. Jetting requirements do not change unless the air density changes.

The motor and carb are at full temp in 5 min of riding.

Quick shot is a waste of time, unless you are having fuel foaming issues on rthym sections.

Remove any one-way vent line on the gas vent hose. Try restarting with the gas cap removed next time.

check for spark the next time the bike dies out on you. If you have lost it, your stator is dying.

 

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Went to work this afternoon and removed the carb and tore it down.  Whoever sold this bike to my boss lied about the carb recently been gone thru by the dealer.  4 of the 7 bowl and a/p screws were seized, and 3 were completely stripped.  After I finally got it all apart, I found the a/p diaphragm very cracked and starting to fall apart.  

 

As far as jets, everything was stock except for a 52 pilot jet.  Still has a 165 main, and factory needle with the clip in the middle position.  Was thinking of dropping the needle 1 notch, being it already has a 52 pilot (45 is stock) and air screw is 3 turns out.  Any advice for settings?  I can get a DG main jet set that has all the 160s main jets in it.  Will be ordering all parts in the morning when I get to work.

Edited by High On Octane

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11 minutes ago, Krannie McKranface said:

45 is the correct pilot jet

The PO probably went to a larger jet to compensate for an air leak, most commonly at the hot start or a bad slide plate seal

The O ring on the hot start is flat and old, so perhaps that is causing the lean condition.  I'm going to be ordering a Proxy carb kit that has new factory jets, needle, gaskets and O rings.

 

Any suggestions for needle position or main jet?  So you think I should go back to a 45 pilot?  Just trying to figure altitude vs. mods vs. Stock jetting.  Thanks, I appreciate the help.  Not new to carb tuning, but am new to these FCR carbs.

Edited by High On Octane

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The hot start needs to bottom out in it's cavity, or it will leak. Clean it out and polish it all up.  The nut is what holds the plunger in place, so if is is cracked, replace it with an alloy one. You can also remove the entire assembly and replace it with a choke assembly.

Your carb kit will most likely not provide the parts you actually need for rebuild, AND the quality of the jets, unless they are Keihin or JD, will be terrible.

You should not need any gaskets either.

By the parts from Sudco, JD Jetting, Yamaha, or Partsfiche.com

Pilot jet

Needle jet (not jet needle)

Apump diaphragm

Slide plate seal

 R&D remote fuel screw

There is never a good reason to go larger than a 45 pilot, unless the motor has non standard mods, or is worn out in the body (leaking air past the slide(, or has a compromised carb body seal (blocking off passages)

 

http://www.dirtrider.com/features/protips/141_0707_keihin_fcr_carb_rebuild/

Edited by Krannie McKranface

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Took another look at my carb today and ordered parts.  I ended up ordering the ProX carb kit.  Claims to have all needed "ethanol resistant" O rings and seals, carb bowl screws, float needle, jets and new needle.  I actually ordered the MSR kit, but low and behold, they are 1 in the same.  My cost was only $26 so figured I'd give it a try.  I wanted to order an actual DynoJet kit but they are on back order, possibly never to be released again.  Also ordered a  new a/p diaphragm kit with a new spring and rod.  The rod looks fine, so may just keep the new one for a spare.  Went ahead and ordered new vent lines as well.

 

Took a peek inside the hot start cylinder and was definitely looking crusty and dirty, so ran a small bore brush in a drill for a few seconds, and it cleaned up nicely.  As for the slide plate gasket, it actually looks in good shape.  It was all there and no deformation, and the slide had very little wear, and could feel it mating well.  So I just cleaned the plate and slide and put it back in.

 

When looking at the microfiche at work, I noticed there are like 10 different factory needles available.  Do you happen to know which one is closest to the DynoJet stage 2 kit needle?  

 

And thanks for the link to the detailed write up for the carb!

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Again, if you order anything but Keihin or JD jetting parts, you will get crap. This includes Prox, Dynojet, and MS. 

"kit's do not have what you need, most of the time, and the jets are not flow tested.

Do not change your needle or main, unless you have an issue. 

The stock main might be a tiny bit too big (big bore = more vacuum), and the needle should not need to be changed.

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Well, you were right.  The ProX kit was pretty mediocre.  But, it did have most of what I needed to get the carb job finished.  Downside was that the O rings for the choke and hot start were too big of an ID, the top cover and bowl gasket were slightly out of spec, but usable.  The jets were definitely out of spec and the needle had a nice taper, but only one notch.  Positive is, that it did come with a good fitting slide plate seal, correct good fitting float valve and new bowl screws.  Also, the main jet was slightly noticeably smaller than the original 165 main jet, but was mentioned that it may be too fat, so went ahead and put that in.  Was unsure about the pilot and slow jet quality, so I left the slow jet that was in there and went down to the 48 pilot jet that I had on hand at the shop.  I broke the O ring on the hot start, so ended up stacking 2 O rings that came out almost perfect. 

 

After re adjusting the idle screw a few times, I got it started.  Let it warm up and played with the air screw a bit, but the motor was hanging up on return to idle.  Decided that the hot start slide was hanging, so put a slight amount of 10-40 synthetic on it and tried again.  Right now, throttle response is crisp with very little popping on decel.  No bogging as of now, but haven't actually ridden it yet.  Plan on taking it out to the track again this weekend for some real testing.  Hopefully the hot stall and painful hot start go away. Also, with the air screw, is out richen, and in lean?  Thanks for your help Krannie.

Edited by High On Octane
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Your carb kit will most likely not provide the parts you actually need for rebuild, AND the quality of the jets, unless they are Keihin or JD, will be terrible.
You should not need any gaskets either.
By the parts from Sudco, JD Jetting, Yamaha, or Partsfiche.com
Pilot jet
Needle jet (not jet needle)
Apump diaphragm
Slide plate seal
 R&D remote fuel screw



Krannie gave you good advice here. I think you should reconsider taking it to improve your odds of fixing your carb issues. Meaning, using other kits and parts will likely prove unreliable.


Well, you were right.  The ProX kit was pretty mediocre.  But, it did have most of what I needed to get the carb job finished.  Downside was that the O rings for the choke and hot start were too big of an ID, the top cover and bowl gasket were slightly out of spec, but usable.  The jets were definitely out of spec and the needle had a nice taper, but only one notch.  Positive is, that it did come with a good fitting slide plate seal, correct good fitting float valve and new bowl screws.  Also, the main jet was slightly noticeably smaller than the original 165 main jet, but was mentioned that it may be too fat, so went ahead and put that in.

I broke the O ring on the hot start, so ended up stacking 2 O rings that came out almost perfect.


This is what I mean by unreliable results from unreliable parts sources.

Please put in one, correct hot start o'ring. Leaks here will lead to a lean condition.

Again, if you order anything but Keihin or JD jetting parts, you will get crap. This includes Prox, Dynojet, and MS. 
"kit's do not have what you need, most of the time, and the jets are not flow tested.


Again. I agree with Krannie's good advice. I urge you to consider taking it to improve your chances.



Took another look at my carb today and ordered parts.  I ended up ordering the ProX carb kit.

Also ordered a  new a/p diaphragm kit with a new spring and rod.  The rod looks fine, so may just keep the new one for a spare.
 
Took a peek inside the hot start cylinder and was definitely looking crusty and dirty, so ran a small bore brush in a drill for a few seconds, and it cleaned up nicely.  As for the slide plate gasket, it actually looks in good shape.  It was all there and no deformation, and the slide had very little wear, and could feel it mating well.  So I just cleaned the plate and slide and put it back in.
 
When looking at the microfiche at work, I noticed there are like 10 different factory needles available.  Do you happen to know which one is closest to the DynoJet stage 2 kit needle?


The Pro X kit can be problematic. Like Krannie (and many, many others), I recommend the JD jet kit. It will come with the correct, high quality parts which will work. They also provide reliable jetting recommendations as well as excellent tech support. Forget trying to duplicate the DynoJet needle. The JD kit comes with two needles, which WILL work great.

Regarding the A/P kit. Use all of it. If you've purchased an updated kit, which are made to address the improper squirt of the original design, the new diaphragm metal center pin and rod are designed to create a precise length for improved squirt action. Use all the new parts. Also, make sure your leak jet is the proper one since this affects a/p squirt

You mentioned you're new to four strokes. They differ from two strokes in that they do not have an air screw, which you've referred to. You'll notice this screw is on the engine intake side of the carb, rather than the airbox side. A two stroke typically has this screw on the airbox side and is called an air screw since it alters air flow. Your four stroke has a fuel screw, named this because it alters fuel flow, not air flow. So. Unscrewing your fuel screw increases fuel flow and richens your idle circuit.

Honestly. I'd start over with a JD jet kit, an R&D flexjet, and all other oem parts, just like Krannie suggested. Float level is also very important.

Good luck, and please let us know how this turns out.
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Thanks for your reply Motrock.  I do have an update.

 

Went up to Rampart Range to do some trail riding yesterday.  Not sure if you're familiar with RR, but it's a bad ass OHV park in the Colorado Rocky Mountains.  Elevation in the City is about 5,200' and the elevation at Rampart is about 8,700', temp ion the mountains was about 60*F.  So, kind of hard to verify whether the bike is where it should be or not.  I can say that once I got the fuel screw dialed in, (Found this out on my own on the trails.  LOL) about 3/4 of a turn out, the bike ran very well.  One thing I'm noticing with this bike, is it does NOT like going slow.  Any speed that causes the engine to fall below the idle speed at about 2K rpms and the bike stumbles however, I am having much less stalls now, and most times was restarting by the 4th kick.  With the exception where I stalled the bike in very technical parts of the trail.  It's hard to kick this tall of a bike when you can barely keep your balance with both feet on the ground.

As for the hot start, I'm pretty confident the way I have it, there are no air leaks there.  The outer O ring I have stacked fills the gap perfectly and was a hair too tight initially.  After I lightly coated the O ring with 10W-40 synthetic oil, adjusted the cable again, the hot start now moves freely, with slight resistance, and I can here it snapping back into place upon release.

 

CURRENT SET UP -

Main - 165 ProX jet (slightly smaller than a Keihin main jet, roughly a 162, guessing)

Pilot - 48 Keihin

Slow Jet - was a 72 stock (IIRC)

Needle - Stock in 3rd position

Needle Jet - Stock

A/P - K&L A/P kit with the stock push rod

Fuel Screw - roughly 1 turn out

 

OVERALL - Bike is definitely running better than it was.  Still has a slight bog on occasion when blipping the throttle fast.  But this bike is a freaking torque monster!  Once rolling at idle speed, the throttle is crisp and the bike just freaking rips.  This bike will stand up on its own without even touching the clutch.  But, I am thinking of getting the  JD kit, however I don't think I can order it from Tucker Rocky or Western Power Sports. If anyone does a TR or WPS part number for a JD kit, it'd be much appreciated!    But, otherwise will likely have to wait until it's in the budget, as I just bought a new Fly helmet, and blew my rear tube on the trails yesterday.  Going to go dink around with the bike this afternoon, will check the plug color and see what it says.  Before, it was very black and carbon coated after about 45 minutes of riding.  I cleaned the plug on a wire wheel bench grinder so I could tell what the new carb changes would indicate without the old carbon still there.

 

So, if I am hearing correctly, the K&L a/p push rod is slightly longer than the stock rod, and should be replaced with the one that came in the kit?  The main reason I didn't was because the push rod is safety wired to the actuator arm.  Wasn't sure what was going on with it so I left it alone.  Is there a reason for this?  Should I safety wire the new push rod as well?  Also, is it possible that the shorter push rod is affecting the low end?  Could it be the cause of my slight low end bog now?  Thank you so much for your help!  These FCR carbs are a bit baffling to me, and still trying to learn everything about them that I can.

 

And as for ordering the ProX kit, it was more of a trail thing to see if the gaskets were of good enough quality to order for customer bikes.  I can get the ProX kit in 2 days, where as ANYTHING from the dealer takes 5-7 business days.  Which leads to customers constantly calling me asking if their bike is done when I don't even have the parts for the repair yet.  But, don't think I'll be ordering those kits again.  The K&L kit fits nicely, but is $42.95 and only has the top and bottom gaskets, float valve and bowl screws.

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OVERALL - Bike is definitely running better than it was.  Still has a slight bog on occasion when blipping the throttle fast......

 
So, if I am hearing correctly, the K&L a/p push rod is slightly longer than the stock rod, and should be replaced with the one that came in the kit?  The main reason I didn't was because the push rod is safety wired to the actuator arm.  Wasn't sure what was going on with it so I left it alone.  Is there a reason for this?  Should I safety wire the new push rod as well?  Also, is it possible that the shorter push rod is affecting the low end?  Could it be the cause of my slight low end bog now?


I haven't made any guesses regarding the K&L A/P Kit, since I'm unfamiliar with it. The rod could be longer or shorter and the rivet in the diaphragm could be longer or shorter than stock. The idea is to allow the accelerator pump diaphragm to alter the amount of fuel going into its bowl and then squirting as the initial charge into the engine intake. Your safety wired ap linkage was a common fix, along with an o'ring mod to force a stronger initial charge into the engine to cure throttle bogging. Around 2007ish, the FCR carb received an updated ap design to accomplish this internally. Your K&L kit may indeed emulate these changes, but you should call and ask them. If so, also confirm with them that you should remove the safety wire with their kit. In any event, you need to use the rod and ap diaphragm they provided together. It's important.

If you were my friend/riding buddy, I'd steal your carburetor and start all over with a JD jet kit, an R&D Flexjet, check your float level and TPS.

Good luck!

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18 minutes ago, motrock93b said:

 


I haven't made any guesses regarding the K&L A/P Kit, since I'm unfamiliar with it. The rod could be longer or shorter and the rivet in the diaphragm could be longer or shorter than stock. The idea is to allow the accelerator pump diaphragm to alter the amount of fuel going into its bowl and then squirting as the initial charge into the engine intake. Your safety wired ap linkage was a common fix, along with an o'ring mod to force a stronger initial charge into the engine to cure throttle bogging. Around 2007ish, the FCR carb received an updated ap design to accomplish this internally. Your K&L kit may indeed emulate these changes, but you should call and ask them. If so, also confirm with them that you should remove the safety wire with their kit. In any event, you need to use the rod and ap diaphragm they provided together. It's important.

If you were my friend/riding buddy, I'd steal your carburetor and start all over with a JD jet kit, an R&D Flexjet, check your float level and TPS.

Good luck!

 

The TPS was actually the very first thing I checked, and was within spec.  I don't remember the exact resistance, but was right in the middle of tolerances, so I didn't adjust it.  Float level appeared to be correct when I assembled it back together, and was very careful not to change it when pulling the old float valve.  Should be 8mm, correct?

 

What is the R&D Flexjet?

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The Fuel screw should be adjusted with every change in air density.

You dont' just turn it to 1.5 turns and then your are done.

You start with a hot motor, lower the idle as low as it will go, and the starting from 1 turn out, raise the idle with the fuel screw.

It should stop going up at about 1.5 turns, but if you try and do this from normal idle, it won't work out, and it will have hanging idle.

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Hey guys, just a little update.  I haven't made any additional changes to jetting, including still using the factory A/P rod.  Took her out to Jewell MX on Sunday and was &%$#@!ing ripping hard!  Played with the fuel screw just a bit, but seemed happiest right at 1 3/4 turns.   In fact, the only 3 times I stalled the bike was in some enduro obstacles, with the slows speeds well below engine idle.  Out on the track, she was screaming.  No bog or hesitation from closed throttle, just nice crisp and raw response.  I came close to some Whiskey Throttle a couple of times too from accidentally rolling the throttle thru some whoops.  I'm very happy with how it is running now.  It does have a slight idle surge, but starting to think that my wear plate might be more worn that I originally thought.  Not bad enough to warrant replacement just yet, but will probably do it this coming off season during a snowy week this winter.

 

Now just need to fix this coolant leak I discovered on Sunday.  Thought is was a bad rad cap, so replace with a 1.6 Helix cap.  Turns out, there is a metal elbow going to the from of the head that must have a bad O ring.  About to post about that in the Yamaha threads.

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