2000 yz426 wont idle and pops on deceleration

6 replies to this topic
  • crazydirthead

Posted July 08, 2010 - 09:48 PM


I know there are plenty of threads on this topic already but I have tried most of the things mention and I still can't seem to fix the issue. Heres the deal, I just bought the bike and it wouldn't idle when I bought it, but I could tell it ran perfect when at 3000+ RPMs. I cleaned out the pilot jet because it was completely clogged and now it will run at a lower RPM but still dies if I completely let off the throttle. Also, when I am decellerating it pops ALOT, I'm not sure how to fix this. I'm almost positive the jets are stock, I know that the needle is. Be gentle on me, I'm new to being my own mechanic. If someone could give me a list of things to check from top to bottom I would very much appreciate it.

P.S. The previous owner did the blue wire mod and it also has a power core IV on it, but I think thats all that is different from stock.

  • grayracer513

Posted July 09, 2010 - 06:26 AM


Start by raising the idle speed. Then adjust the idle mixture.


Check the exhaust for loose clamps, etc. before blaming the popping entirely on the carb.

  • iPilot

Posted July 09, 2010 - 09:35 AM


+1 on the idle speed adjuster _and_ idle mix adjuster.

there are aftermarket idle mix needles out there for around 20$ at cyclegear and many other stores that have a knob on them to eliminate the need for a small screwdriver so you can make adjustments by hand as you ride.

in most cases i dealt with, popping out of the tailpipe on engine braking was caused by incorrect idle mix (since that's the main thing regulating fuel while throttle is "closed") and usually excessively rich. slightly rich is ok, it will give you better throttle response and might rumble very slightly on prolonged engine braking. but those are just my experiences wit the issue :)

If the pilot jet was clogged, i wouldn't discount that the idle mix screw passage might be clogged as well (and maybe other things). When i got my 426 one of the first things i did (leaky carb induced) was to completely disassemble the carb, wash it, blow it out with air and (change few o-rings) reassemble. after a little bit of messing with idle speed/mixture it works great so far! *knock on wood*

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  • gdbarr1976

Posted July 09, 2010 - 10:53 AM


Take the float bowl off and make sure the seat, as in the hole the bottom of the carb for the needle valve, is good and clean. If it has any crud in it the needle may stick and not let enough gas get into the float bowl.

  • crazydirthead

Posted July 19, 2010 - 10:47 AM


thanks guys, I got it going great now, idles low and doesnt pop at all.

  • whiteghost

Posted July 21, 2010 - 05:30 PM


What did you do???

  • crazydirthead

Posted July 22, 2010 - 11:09 AM


1. I cleaned all the jets, which is super easy if you have any brain at all, they are all on the bottom of the carburetor.
2. I cleaned the needle, It had some film on it that I think might have been making it work incorrectly, it's easy as well, on the top of the carb is where you get at it from.
3. I adjusted the idle screw to 1 and 3/4 turns out (was at 1).
4. Retightened my exhaust clamps.

That stopped the popping but it still wouldnt idle well until I adjust the idle screw, which is the black knob on the side of the carb (not the choke). It's important to make sure the bike is warm before adjusting the idle screw, otherwise it still wont idle right once it's at operating temperature.

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