Help please with tuning my bike

Ok here goes....My 02 426 is acting up. It is topping out way too soon, seems like it's full throttle at 1/3 throttle. Classic signs of an air leak and/ or lean jetting right? Well I've tried to find an air leak and can not find one anywhere. Jetting is as follows:

Main 170

Pilot 42 (was using 45 for a long time but it had same issues lately plus hard starting)

Needle JD Blue clip in #5 position from top down

All else is stock in carb.

Adjusted the AP squirt and did oring mod today. Didn't help my problem.

Bike has Hotcam auto decomp exhaust cam,FMF powerbomb and FMF Q4 (newer version custom fit from a 450).

Test rode the bike today, it is FAST but almost too fast and out of control.

I've tried all I can think of triple checking everything like timing and such. What am I missing here?!

I guess the best way to describe it is like if you were to pull the hot start and rev it. It's not a smooth powerband, it just takes off and revs out right away. I guess it could be something electrical also?

I know you can't really go by spark plugs with fuels nowadays, but I just checked mine out and it is a nice tan color on the porcelain with black soot on the very end of the threads. Better than white I guess...

Ok here goes....My 02 426 is acting up. It is topping out way too soon, seems like it's full throttle at 1/3 throttle. Classic signs of an air leak and/ or lean jetting right? Well I've tried to find an air leak and can not find one anywhere. Jetting is as follows:

Main 170

Pilot 42 (was using 45 for a long time but it had same issues lately plus hard starting)

Needle JD Blue clip in #5 position from top down

All else is stock in carb.

Adjusted the AP squirt and did oring mod today. Didn't help my problem.

Bike has Hotcam auto decomp exhaust cam,FMF powerbomb and FMF Q4 (newer version custom fit from a 450).

Test rode the bike today, it is FAST but almost too fast and out of control.

I've tried all I can think of triple checking everything like timing and such. What am I missing here?!

I guess the best way to describe it is like if you were to pull the hot start and rev it. It's not a smooth powerband, it just takes off and revs out right away. I guess it could be something electrical also?

I know you can't really go by spark plugs with fuels nowadays, but I just checked mine out and it is a nice tan color on the porcelain with black soot on the very end of the threads. Better than white I guess...

You have to do tests under load. A free reing engine will hit redline at 1/4 throttle.

You main jet is also way rich, Should be more like a 160. Your needle is very rich too....Unless you ride in death valley in 30 F degree temps

Yeah I have ridden it, not just doing tests on the stand. Either way it acts like I'm full throttle before I even get to half throttle. It's like a ghost put on a 1/4 throttle kit while I was sleeping one day.

I know the jetting is somewhat rich on the needle, I don't think it is on the main. JD jet kit that I have recomends a 170 as a starting point and I have run with no problems in the past. I am one clip position richer than recomended. That's why I know it has to be some other type of issue and not the jetting.

Does the bike run properly at small throttle openings? Then when you get to say 1/4 throttle, it suddenly takes off?

I have the same bike and the same problem. My needle is 170 but set at 3rd spot from the top. My brother in law said to check the accelerator pump. Anyone have any input on that?

Yeah I would say it runs good until you get to 1/4 throttle, maybe just past that. It starts and idles fine, seems to be better with the stock pilot back in. I did check the accelerator pump it works good, rubber diaphram is good and it squirts without hitting the slide.

First off, do not mix things up. The key to resolving a carb is to work on one area, get it right, then move on. Get your pilot/fuel screw set right then leave it alone.

Here is the quick/Cliff notes version of Jetting:

Fuel Screw/Pilot Jet

Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method. Do it with the bike fully heated up.

Gently turn the screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly). Once warmed, slow the idle to the lowest possible speed.

*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***

Turn the screw in until the idle becomes rough or the bike stalls.

if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.

If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.

Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.

If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.

If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.

If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,800 rpm, but go by the spec in your manual.

Be sure to keep notes of your settings. You may find you need to make a change, say if you're riding in the mountains or down at the beach. Returning home, it is a simple matter of referring to your notes to restore things.

Main Jet

Starting with the recommended main, remove the airbox door and go for a ride (bike fully warmed up, 3rd or fourth gear, up a slight hill). Is it better or worse?

If it is better, you need a smaller main.

Go down one size, replace the airbox door, ride. Remove the airbox door and test again. Better or worse? If better, go down a size again. Keep repeating this till the test with the airbox door is worse.

If it was worse with the airbox door removed, tape over 1/3 of your airbox opening, test (airbox door on, of course).

If it is worse now with the tape and was worse with the airbox door off, your main is just right. You are done!

If it seems better, you need to go up a size in main jet. Then test it again (remove the tape). Replace the tape, test again. If with the tape on it is better, go up another size in main. Keep repeating this till having the tape on is worse than with it off.

To finish up and ensure you are set accurately, retest the bike with the tape off (airbox door on), ride it, then remove the airbox door (tape off, of course). Best performance should be with the airbox untapped, airbox door on.

Remember, the main only operates at WOT. Ideally, you want to be in 3rd or 4th gear doing the tests, hitting max revs (just shy of the limiter) for at least 10 seconds to get an accurate representation of the jet status.

Be sure to keep notes of your settings. You may find you need to make a change, say if you're riding in the mountains or down at the beach. Returning home, it is a simple matter of referring to your notes to restore things.

The Needle:

First, confirm your TPS is adjusted correctly per the manual.

To do this, you need to mark the throttle grip. I place tape on the grip and a piece on the throttle housing. I make a mark on each. I open the throttle completely and then make a mark to correspond to that. Then I make a series of marks at 1/2, 1/4, 3/4, 1/8,3/8, 5/8 and 7/8.

Again, in third/fourth gear ride up an stead incline each time at one of the positions, make notes on how it runs at each.

If there are running issues in the first 1/4 throttle, you will need to try a different needle, one where the last letter is different. As you go up in the alphabet, you go leaner.

If there are running issues above 1/4 throttle, that deals with needle taper, length and clip position. Often just moving the clip will sort things. If a different needle is needed (say you ran out of positions) the second to last letter is what is changed. A letter is typically equal to a clip position, so an one letter change is like moving the clip on spot.

Remember, dry sounding or flat (not a bog, just flat/lack of power) is lean. Wet, misfires, heavy is rich.

Here is a more indepth guide you can download:FCR-Tuning Guide

So Get your pilot right and the fuel screw. Tell me, is this problem new or has it always been there? If it is new, what happened/did not happen prior?

It is a new problem that just happened while riding one day. I richened up the needle to make it better than it was, but it still was not like it used to be. I shouldn't have to run the JD blue needle on the richest setting.

It definitely does not bog like a rich condition. But it doesn't sound dry or flat either. It revs too quickly so to say and vibrates more than usual also.

Ok, knowing it suddenly happened is VERY important. Put your jetting back to how it was prior to the problem. Jetting does not magically change during a day.

There really is ony a few parts that can wear or fail in your carb.

Needle Jet Emulsion Tube - Remove and inspect for signs of 'ovalizing' with a strong magnifying lens

Carb Slide - Inspect seal and vacuum release plate for signs of cracking

Confirm no vacuum leaks exist - Cracked manifold, faulty hot start, ect.

Ok I will check the slide again and the emulsion tube. I have checked the manifold for cracks and leaks and can not find any. I also checked the hot start and pulled it out to make sure it was working properly, it is. How do I check for vacuum leaks though? Is there a place to measure vacuum?

Spray brake parts cleaner over the manifold and carb with the bike running. If you get a change in RPM, you have a leak.

Also inspect the float needle valve, and float height.

When the bike is running, is it smooth or are there and misfires?

Yeah I have done the sparying checking for leak test, no change. I also checked the needle valve it is in good condition, the float level is 8-9mm which is the spec (hard to get an exact measurement but it also lines up with the carb body as it should).

Actually after thinking about it my bike starting running this way after I rebuilt the petcock and changed out the oring on the seat. Sorry it's been a while since I did all this, have other toys and this one has been sitting for a while. The carb is spotless does not need any more cleaning so the sitting isn't the issue.

I replaced all the seals in the petcock and the oring that is on the removable seat (the seat part of the needle/ seat). I had a small leak out the overflow while it sat, turned out to be a bad oring on the seat allowing more fuel to get to the bowl after the needle closed off the flow. I rebuilt the petcock just because, thinking it may need it also.

I have good flow out of the fuel line with the petcock open.

So how could replacing these parts change the way my bike ran? I am guessing that the bad oring overflowed the bowl a little causing a rich condition? That's the only thing I can think of. But still why would I need jetting to be more rich than I already have it especially on the needle clip position? It's already on the 5th from top which is richer than most run it and than what JD recomends.

I checked the seal on the slide and the manifold again....both good.

Not the float needle, the needle jet emulsion tube, the part teh slide needle goes in and out of and the main jet is screwed into.

If the float needle valve was not fully closing or leaking, you would probably get drips out the overflow with the bike not running, petcock on. You might have an overly rich condition at idle that would go away as rpms rose.

The slide is not worn, the release plate not cracked?

I have a WR and YZ and they are a little finicky about valve clearances. They dont have to be adjusted often but they run terrible and are hard to start when they get too tight. It might be possible that you addressed a valve clearance issue with some jets... Anyone agree?

No slide is in good shape. I haven't inspected the emulsion tube yet, but I saw you metnioned the float valve in your last post and that is what I was responding to.

After all I have inspected I think it may be a clogged pilot jet. The 45 I had in there doesn't seem to want to come clean. It's hole is smaller than the 42 so I am guessing I need a new 45. I had put the stock 42 back in but maybe that is just too lean. I couldn't get the fuel screw to make much difference at all, I do have the easy adjust one. Since everything else checks out, I will get a new 45 pilot and see how that works out.

I just checked the valve clearance yesterday and it is right in the middle on all 5, just the way I set it when I made my first adjustment finally last year. I had to adjust 1 intake and 1 exhaust.

Intake clearance .13mm. .10 fits and .15mm doesn't, therefore it's in the middle.

Exhaust clearance is the same only .23mm as .20mm fits and .25mm does not

I knew you would have checked your clearances when you did your hotcam, but wasnt sure how long that was. Sounds like you eliminated that. You may be on to something with the pilot jet...

Ok test rode it again today and still having the same issues. I replaced the intake boot as the stock one had a suspect crack that goes half way through, but still no change in idle with the carb cleaner test with either boot. I also replaced the seal that is on the slide in the carb just because, the stock one seemed ok but new one seems better. Put in a new 45 pilot as the older one was a bit plugged. None of these changes made any difference. I have played with the jetting from pilots to needles to clip positions to mains richer and leaner. Gets worse if I go leaner but even going way rich doesn't help.

I am convinced there is no air leak and that it also isn't a jetting issue. I'm thinking electrical? Like timing or the TPS possibly? I bench tested the TPS and could not get a reading on it no matter the throttle position. That tells me it's bad I would guess. I ran the bike with it unplugged and it ran the same way.

I've also read that others have unplugged it and their bikes still run as good as plugged in.

SO WHAT THE HECK IS WRONG HERE?

There is no more cruising on my bike, anything over 1/8th throttle is hauling A**!

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