2000 yzf426 with powerbomb and q exhaust.

10 replies to this topic
  • miketkach

Posted February 11, 2009 - 01:31 PM


I have a bog and it stumbles with quick snap off idle. Can anybody help me with jetting. I ride under 2000 feet. currently running stock needle 4 groove, 45 pilot and 165 main. This is what FMF recommends. It runs super other than that. Grabs revs real quick. I hate the stumble, big time. please help me!!!

  • grayracer513

Posted February 11, 2009 - 02:27 PM


First you need to learn not to give it a quick snap off idle. Roll the throttle open, more slowly at first and faster as the engine responds. After a while you'll do this reflexively, and your engine will seem much more responsive with you causing it to stumble.

Second, read up on this:


  • miketkach

Posted February 11, 2009 - 03:17 PM


thanks for the tip. I am used to two stroke bikes I suppose

  • grayracer513

Posted February 11, 2009 - 04:10 PM


It's a skill thumper riders have had to learn since the dawn of time. It was a bigger problem before bikes started coming with accelerator pumps. Even so, there's the normal amount of stumbling, and a point where it's abnormal. Having the pilot set correctly and the pump timing right helps. Read the link.

Another nasty two-stroke habit that you've apparently more or less gotten over, since the bike has started for you at least once, is the twist as you kick maneuver everyone seems to put so much stock in. If you start twisting the throttle as you kick a 426, it will do nothing but give you a lot of exercise. Learn to hold the throttle off, or at one steady, very small opening. Never twist as you kick.

  • miketkach

Posted February 11, 2009 - 08:03 PM


I ride a CR 500 in the dirt. My 426 is actually dual sport. It is real cool! I also ride an XR 650R dual sport. Of course that is a totally different animal al- together. I got that info on the mod and it was very well presented. I will let you know how it works out.

Thanks again!

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  • Dano426

Posted February 12, 2009 - 08:11 AM


I would also try the o ring mod and a smaller leak jet. It work for me


http://www.thumperta...hlight=ring mod

  • grayracer513

Posted February 12, 2009 - 09:32 AM


I would also try the o ring mod and a smaller leak jet. It work for me


http://www.thumperta...hlight=ring mod

Neither of these apply to a 426. The 426 has no leak jet , for one thing. For another, the stumble in the 426 is more often cause by a hyper-aggressive accelerator pump than a weak one, which is why the BK mod works so well on them.

  • miketkach

Posted February 12, 2009 - 11:07 AM


gray, how is it you know so much about the 426. Or is it just understanding all bikes?

  • grayracer513

Posted February 12, 2009 - 12:37 PM


I was a professional motorcycle mechanic/fabricator/machinist for many years, followed by a long career as a engine/transmission/engine control systems technician with Ford and then Chevrolet. That, and I collect information the way your crazy aunt collects spoons.

  • Brandon Meidam

Posted February 23, 2009 - 09:28 AM


I had a 2001 426 with the FMF Q and never could get it to run right after many hours messing with the carb. I put my stock pipe on just for a test and it ran perfect. The FMF Q has too much backpressure for these bikes. They need to breath to run right.


  • miketkach

Posted February 25, 2009 - 07:07 PM



I did the mod as suggested by Grayracer513 and it is perfect. Thanks Gray you are a kingpin and a gentlemen.

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