FCR40 Tuning Woes- XR600R

Hi guys!  Long time lurker, but I don't believe I've actually ever posted here prior to today.  My XR journey began in December of 2013 when I picked up a gorgeous 99 XR650L from someone who was leaving the country the next day and absolutely needed it sold for rock-bottom price.  I got hooked, and wanted more.  My best friend bought an XR650R, but not wanting to deal with the extra weight and liquid cooling, I bought a CA street legal XR600R a month ago for $1500.  It's a 95 in reasonably good nick, burns a bit of oil and the PO had never done any maintenance, so, among other things, I bought a UNI filter for it, which has been oiled and installed.  I also had an FCR40 that I bought for my XRL, but when I bought this bike I decided to throw it on here since I plan on transitioning the L into more of a touring dual-sport and having this as my hardcore dirt machine.  Also, this is my fifth bike- I have two YZF600Rs, one for commuting and one for the track, and a V-Strom 1000 for long-distance super-touring duty.  I may be a bit of an addict.

 

So, intros out of the way (nice to meet you all in advance!), I have this FCR carb.  I cleaned it top to bottom, installed new jets as per the excellent "complete guide" thread here on TT (45/158, NCVT on the 3rd clip, starter and air jets left as they were (I think 72 and 100 is what their values were)), set the float height to 9mm (it was around 14 when I got it, carb came off a 2003 CRF450R), fashioned an adapter from PVC and rubber hose so I could mate it to the airbox, installed an XR650L insulator, and hoped to be good to go.

The problem is, it won't idle unless the fuel screw is four turns out.  Hmm, I thought to myself, the motor is (presumably) completely stock, so it shouldn't NEED a larger pilot, but we'll try it anyway.  48 goes in, no dice, still requires four turns, sputters and dies at 3.75.  50 goes in, same.  I've tested up to a 55, and the bike STILL will not idle with the fuel screw set to fewer than four turns. 

 

Does anyone have any tips?  The bike feels ok with a 45 in at four turns, it will pull hard at mid- and full-throttle, and it feels ever so slightly worse with a 55 in it, so I am pretty sure that the 45 is correct and there's something odd going on.  To that point, when I replaced the stock fuel screw with an aftermarket one (for ease of turning), I found a tiny chunk of o-ring in the hole, which I extracted.  Is it possible that there's a chunk of something in the tiny passage between the idle screw hole and the pilot jet hole?

 

Any ideas would be GREATLY appreciated!  I'm starting to tear my hair out over this... I don't want to put the stock carb back in, but if I can't get this FCR tuned up... :(

Edited by aTuWitty

Sure you float is set right? 

I cut a piece of cardboard into an L shape (stenciled off of a 90 degree angle, so not eyeballed), the cut was measured to 9mm with a micrometer, and set according to that.  It could be wrong, as it's the first time I've ever set the float height on a carb before, but I set it to 8mm before (based off some erroneous advice) and then changed it to 9mm, and it made no change in the way it reacted.  

It's possible your PVC adaptor is causing weird air flow. Try removing the adaptor and running it with the intake end of the carb just open and unfiltered.

When checking float height, are you certain you weren't compressing the spring loaded plunger?

It's possible your PVC adaptor is causing weird air flow. Try removing the adaptor and running it with the intake end of the carb just open and unfiltered.

When checking float height, are you certain you weren't compressing the spring loaded plunger?

Quite certain.  I'll try it without the adapter today.  Also, if I WERE compressing it, wouldn't that create a rich condition, necessitating fewer turns on the fuel screw?  I'm a total noob when it comes to carb tuning, so I could be 100% off, and if so, please let me know :)

SAME problem. 88 600r with 628 piston. Stock air box. Super trapp muffler. PVC adapter carb to box boot. Fcr39

I've tried exactly how my 95 600r with stock bore, pod filter no air box, and power core 4 muffler, was jetted. NCVT 3rd clip, 45 pilot, 160 main. It fired but idle was all the way up and you needed to flick throttle to keep it running. My 95 has an fcr41 tho, the 88 is an fcr39.

Tried with air box and without.

Figured pilot.

Went to 48/165

I can't personally kick it cause my leg injury but the neighbor kid will help me again. He started it the first time. I tried to kick it with the 48 but my kick is bad. I need the youngen with two good legs. I can't start my rmz250 cold, warm yes. But my 95 starts and runs perfectly. It is lower on street gear but starts easy.

Oh and when the 88 started on the 45 pilot it was with Airbox,without filter and starter fluid spayed into intake while kicking full throttle. Decomp, tdc, a hare past, and WOOM!

Plugs wet, exhaust puffs smell like gas, I've confirmed spark twice! And at TDC it's like stone so I think there's compression. Valves are perfect.

This is an AFR thing.

Thinking about going to 50.

I'll let the kid try and kick the 48 first.

I'm staying posted on this

Best of luck.

Oh and I'm sea level, 70degrees F, 91 pump gas

Quite certain.  I'll try it without the adapter today.  Also, if I WERE compressing it, wouldn't that create a rich condition, necessitating fewer turns on the fuel screw?  I'm a total noob when it comes to carb tuning, so I could be 100% off, and if so, please let me know :)

I don't remember the FCR specifically, but generally the float will be fairly parallel with the carb body lower lip when the adjustment is correct. Sometimes the seam of the float, sometimes the bottom surface. Even a misadjusted float shouldn't throw off the pilot jettting by 5 sizes.

It is very possible that your mixture screw channel is clogged. Have you blown it clear with carb cleaner and compressed air, in both directions, to verify the channel is open?

Are you using an aftermarket mixture needle? They can be inaccurately machined.

Oh, and you guys are getting the engine fully up to temp before adjusting the jetting, right? As in probably 10 minutes of riding time, not just idling on the stand.

And remember these engines are cold blooded. It's normal for the cold idle speed to be much slower. I give the idle speed knob a half twist faster when cold starting, then adjust it back down when the engine has warmed to the point that the idle speed is slowly getting faster and faster.

Edited by heart_of_darkness

SAME problem. 88 600r with 628 piston. Stock air box. Super trapp muffler. PVC adapter carb to box boot. Fcr39

I've tried exactly how my 95 600r with stock bore, pod filter no air box, and power core 4 muffler, was jetted. NCVT 3rd clip, 45 pilot, 160 main. It fired but idle was all the way up and you needed to flick throttle to keep it running. My 95 has an fcr41 tho, the 88 is an fcr39.

Tried with air box and without.

Figured pilot.

Went to 48/165

I can't personally kick it cause my leg injury but the neighbor kid will help me again. He started it the first time. I tried to kick it with the 48 but my kick is bad. I need the youngen with two good legs. I can't start my rmz250 cold, warm yes. But my 95 starts and runs perfectly. It is lower on street gear but starts easy.

Oh and when the 88 started on the 45 pilot it was with Airbox,without filter and starter fluid spayed into intake while kicking full throttle. Decomp, tdc, a hare past, and WOOM!

Plugs wet, exhaust puffs smell like gas, I've confirmed spark twice! And at TDC it's like stone so I think there's compression. Valves are perfect.

This is an AFR thing.

Thinking about going to 50.

I'll let the kid try and kick the 48 first.

I'm staying posted on this

Best of luck.

Oh and I'm sea level, 70degrees F, 91 pump gas

Wet spark plug and gas smelling exhaust both indicate too rich. You'd need to go a step leaner on the pilot.

I thought it was from kicking so much, so leaner than 45? The fcr came with a 42 and it felt and sounded the same and didn't start. That's why I thought going up to 45 like my 95 has would do it. It DID start, idle screwed all the way in it still bumbled, you needed to crack throttle. It's had a couple full throttle flicks. But hasn't been ridden and definitely hasn't reached operating temp yet.

I can't even start it. It's been decompressed and kicked a hundred times with 42, 45, and 48...

LEANER than 42???

I don't remember the FCR specifically, but generally the float will be fairly parallel with the carb body lower lip when the adjustment is correct. Sometimes the seam of the float, sometimes the bottom surface. Even a misadjusted float shouldn't throw off the pilot jettting by 5 sizes.

It is very possible that your mixture screw channel is clogged. Have you blown it clear with carb cleaner and compressed air, in both directions, to verify the channel is open?

Are you using an aftermarket mixture needle? They can be inaccurately machined.

Yeah, that's what I had read about the float height, and that's basically where it's at- seam on the float parallel with the carb gasket mating surface, which is where it is now.

 

I have blown everything I can blow and shot cleaner into everything, but I wasn't able to verify that air was getting through the tiny channel between the pilot hole and the mixture screw hole.  Both the pilot jet hole and mixture hole are clear, though- I can see through the mixture hole and was able to run a tiny piece of wire through the pilot hole.  How would one go about clearing that tiny channel between the two holes, if it is clogged and compressed air won't do it?

The fuel screw is a Trackside model- http://www.amazon.com/TRACKSIDE-Air-Fuel-Mixture-Screw/dp/B00C4YRRYW

Appears visually identical to the stocker when held next to it.

 

Oh, and you guys are getting the engine fully up to temp before adjusting the jetting, right? As in probably 10 minutes of riding time, not just idling on the stand.

And remember these engines are cold blooded. It's normal for the cold idle speed to be much slower. I give the idle speed knob a half twist faster when cold starting, then adjust it back down when the engine has warmed to the point that the idle speed is slowly getting faster and faster.

I haven't ridden it for 10 minutes at a time since the stock carb was in it >.<  I just figured that it would idle somewhat similarly to my XRL, which will fire up on choke under any ambient temp and then you can drop the choke and it will idle just fine.  When I say it won't idle, I mean that it literally will sputter and die if the fuel screw is turned to 3.75 turns from four!  I have had it idling for minutes at a time, and ridden it for probably 3-4 minutes at a time, so it's not completely cold.

Edited by aTuWitty

You guys need to get your engines really fully up to temp. These are big, cold blooded engines that run much differently when cold. Plus the FCR, which allows running a crisper pilot jet than the stock 600R carb, is even more so.

I've seen an aftermarket fuel screw that was minutely off, just enough that the number of turns was significantly different than the stock screw. So if you experience strange mixture behaviour, verify with the stock screw.

I'm using an MSR screw, same as my 95, same as my rmz, no problems. I've tried stock screw too on this 88 before I had the MSR screw.

HoD, how am I supposed to get up in temp?

My 95 starts no problem. 30 seconds ago it was just running and 5 minutes ago I was kicking that 88. You can hear you're kicking on the right stroke like on my 95.

HoD, should I go leaner? Try a 40? I've tried 42, 45 and 48.

I've tuned my rmz250, tuned my 95 600r, tuned my bosses crf450r race bike, and his yz450f supermoto race bike. I've been in some fcr's. This shouldn't be this hard for me.

But my injuries play a part...stuff is harder for me to figure out with a brain injury.

I'll get a 40 tomorrow if you think that'll be the mixture that'll work.

It's not really modded, super trapp muff and a 628cc piston. Stock intake.

My 95 is stock bore. Pod box less filter and fmf power core 4.

I'll sonic clean it again, and try a 40 this week.

I want to add, when it did run, you couldn't let it idle with no throttle. Idle screw turned all the way up and it sounded thirsty. Like when I fill throttle flicked it sounded good. Just won't idle. That told me go richer...I should get a 40 and a 50, try richer and leaner, I'll get the neighbor with a good leg to kick her. Thoughts?

I think our issues are similar.

Edited by notoriousE-R-I-C

You guys need to get your engines really fully up to temp. These are big, cold blooded engines that run much differently when cold. Plus the FCR, which allows running a crisper pilot jet than the stock 600R carb, is even more so.

I've seen an aftermarket fuel screw that was minutely off, just enough that the number of turns was significantly different than the stock screw. So if you experience strange mixture behaviour, verify with the stock screw.

Perhaps I'm not making my skepticism clear- the XR600R motor is extremely similar to the XR650L motor, correct?  The XR650L has no issue starting and idling, even at a cold idle, in these temps (low 70s here in Cali).  The XR600R motor that I'm working on will not idle at all unless the fuel screw is set to four turns out, regardless of the pilot I've used.  I understand that the bike idles differently when up to temp vs when cold, but if you're saying that I have to get the motor up to temp in order to get the fuel screw back in to 2.5, something is very wrong.  I shouldn't have to run the bike for 10 minutes just to get the bike to idle with a normal fuel screw setting (because I'd have to do that every time I rode the bike).

Does that make more sense?  I'm not doubting you, in fact I agree that the bike idles differently when warm vs when cold, but my issue is that it shouldn't have that big of an effect (at least, not big enough to cause significant change to what I'm working with here).  I'm just theorycrafting here, and I'll give getting the motor nice and hot a shot tomorrow.

Also, what is "up to temp"?  I don't have an oil temp gauge.  It's gotten hot enough sitting in my driveway that water evaporates off of the cooling fins (and that has made no difference in its starting/idling).

[edit] I don't want this to sound adversarial- I guess my main question is, what would getting the engine up to temp tell me?  I don't see how it could reveal any problems with the setup.  Please enlighten me :) [/edit]

Edited by aTuWitty

Perhaps I'm not making my skepticism clear- the XR600R motor is extremely similar to the XR650L motor, correct? The XR650L has no issue starting and idling, even at a cold idle, in these temps (low 70s here in Cali). The XR600R motor that I'm working on will not idle at all unless the fuel screw is set to four turns out, regardless of the pilot I've used. I understand that the bike idles differently when up to temp vs when cold, but if you're saying that I have to get the motor up to temp in order to get the fuel screw back in to 2.5, something is very wrong. I shouldn't have to run the bike for 10 minutes just to get the bike to idle with a normal fuel screw setting (because I'd have to do that every time I rode the bike).

Does that make more sense? I'm not doubting you, in fact I agree that the bike idles differently when warm vs when cold, but my issue is that it shouldn't have that big of an effect (at least, not big enough to cause significant change to what I'm working with here). I'm just theorycrafting here, and I'll give getting the motor nice and hot a shot tomorrow.

Also, what is "up to temp"? I don't have an oil temp gauge. It's gotten hot enough sitting in my driveway that water evaporates off of the cooling fins (and that has made no difference in its starting/idling).

[edit] I don't want this to sound adversarial- I guess my main question is, what would getting the engine up to temp tell me? I don't see how it could reveal any problems with the setup. Please enlighten me :) [/edit]

Your thoughts seem valid, and I don't claim any particular expertise. I have spent plenty of time fiddling with jetting on my FCR conversion, and with the stock 600R carb before that.

Witty, your problems may be a clogged passage or wonky mixture screw. It may not be just the pilot jet size. With a large enough pilot jet the mixture screw could be nearly closed off and the bike will idle.

When these engines warm up, the idle speed will slowly rise even without any jetting or throttle changes. Engine heat has a catalytic effect, warmer oil has less drag, internal part tolerances change, etc. You'll have endless frustration trying to jet when your engine is in that half warm transition period, because all the parameters are constantly changing.

The factory 600R carb lacks an accelerator pump, so the bikes run rich pilot jetting to compensate. Rich pilot jetting happens to also give the necessary enrichment for a cold engine. Plus the butterfly style choke seems to work more progressively than the FCR's plunger style enrichener. The 650L carb is a different CV design, and I think the Dave's mods jetting specs are for a fairly rich pilot jet.

Edited by heart_of_darkness

Gotcha!  One thing that IS a bit odd to me- at 2.5 turns, the bike will almost always start up under choke, regardless of the pilot I've got in there.  When I have the fuel screw out to four turns, where the bike idles without choke, the choke causes the RPMs to shoot up to almost 4k, which just seems... wrong!  I guess I don't understand how the choke works on this one vs on my 650L, but the 650L choke only raises the RPMs by maybe 1k or so... 

Today I'll replace the fuel screw with the stocker, run it till it's crazy hot, try running it without the carb adapter, etc.  If it IS a clogged passageway, one of the tiny ones that I can't see through or put a wire through, how would I go about fixing that?  Probably with an actual, legit air compressor, as opposed to the canned air I've been using (which is all I currently have access to, sadly)?

The FCR choke is a plunger style enrichener. I think it works by both adding fuel as well as enough air to raise the idle very noticably. The 600 carb is a butterfly that only richens the mixture, which I prefer.

I haven't tried jetting the choke, but yes it is too enthusiastic about its job. My starting procedure is to get the engine started on full choke, then immediately reach down and manually hold the choke knob at about a half choke position. I think some models of FCr had a half choke detent position. Or you could run a cable and handlebar lever, which would be easier to modulate.

I'm using an MSR screw, same as my 95, same as my rmz, no problems. I've tried stock screw too on this 88 before I had the MSR screw.

HoD, how am I supposed to get up in temp?

My 95 starts no problem. 30 seconds ago it was just running and 5 minutes ago I was kicking that 88. You can hear you're kicking on the right stroke like on my 95.

HoD, should I go leaner? Try a 40? I've tried 42, 45 and 48.

I've tuned my rmz250, tuned my 95 600r, tuned my bosses crf450r race bike, and his yz450f supermoto race bike. I've been in some fcr's. This shouldn't be this hard for me.

But my injuries play a part...stuff is harder for me to figure out with a brain injury.

I'll get a 40 tomorrow if you think that'll be the mixture that'll work.

It's not really modded, super trapp muff and a 628cc piston. Stock intake.

My 95 is stock bore. Pod box less filter and fmf power core 4.

I'll sonic clean it again, and try a 40 this week.

I want to add, when it did run, you couldn't let it idle with no throttle. Idle screw turned all the way up and it sounded thirsty. Like when I fill throttle flicked it sounded good. Just won't idle. That told me go richer...I should get a 40 and a 50, try richer and leaner, I'll get the neighbor with a good leg to kick her. Thoughts?

I think our issues are similar.

Start with Dot Com's recommended #45, mixture screw 3 turns out (probably a little rich), get the engine started and really fully up to temp, and only then adjust the mixture screw.

And again, expect it to need a while of choke or partial choke.

Ok I'm feeling on another sonic bath for it. It's easy to do, just strip the carb. If you're jetting you're a third of the way there. I'll throw the 45 back in and try 3 screws out on the screw.

Here's my question. On any fcr I've touched I've never changed a starter jet. What is its role? Numbers up means hole is bigger? Mines a 72. I did nothing to my 95s fcr starter jet.

Also expert advice has steered me towards trying the CDI off my 95 and give it a try.

My 45 was brand new.

My 42 and 48 have been sonic bathed.

Whole carb has been sonic bathed.

Fuel screw and o ring are MSR and brand new.

Unfortunately probably won't find time for this until Thursday. Might hire the neighbor kid, he helped build my 95. He build vintage trucks now.

I'm staying tuned to you Atu!

It doesnt make any difference what bike the carb came off, the float height should not have needed adustment.  The proper way to set it is to take the float bowl off and tilt the carb so that the float just rests against the check valve but not compressing the spring tip of the check valve.  The float should be parallel with the float bowl mating surface.  If you want to just check the float fuel level with the carb installed, remove the black pipe used to drain the float bowl and replace it with a clear tubing and route it upwards to the top of the carb.  Open the drain screw and the fuel should level off in the tubing indicating where the float is set.  The fuel level should be right at the mating surface of the float bowl to the carb body.  Adjust accordingly.  

 

A #45 Pilot seems large for a nearly stock engine

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