Engine stumbles badly when landing from jumps

4 replies to this topic
  • newyzguy89

Posted May 06, 2014 - 01:54 PM


My engine stumbles VERY badly when landing from jumps and trying to accelerate for the next jump. The bike runs good in general with just this one major hiccup. I have taken the carb apart and cleaned it with chemicals and air, the BK mod is done, the accel pump timing is spot on, different jetting that I have tried doesn't seem to affect it.

I have a no-toil air filter w/o screen, white bros. exhaust (soon to be FMF), the carb has been to Zip-Ty for their mods. Last year, at the recommendation of a former Yamaha racing mechanic I raised the float level very high and the problem went away, only to come back now.

Anyone have any experience with this and an idea how to make it go away?

  • crb357

Posted May 06, 2014 - 05:37 PM


Have you checked the float to see if it has moved away from your spec?

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  • grayracer513

Posted May 07, 2014 - 06:52 AM


Year model, please.  No one here is psychic.

  • newyzguy89

Posted May 07, 2014 - 01:43 PM


Sorry, thought I had that in my signature, didn't even look. 2002 YZ426

  • Thommo_400f

Posted May 09, 2014 - 01:33 AM


My 400 had similar symptoms.
Turned out no jetting could fix it.
The mid body gasket had gone bad over the years. Only option was to get another carb because at the time I didn't know how to fix it...

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