spark plug problem

awilson40 · Sep 15, 2002

My 89 kx 125 has always had this problem, even after a new top end, lower end, seems jetted fine and it runs great. However, If I run it hard and shut it down, then restart it the plug will foul. Not totally, just enough to make the bike bog on low end and it wont clear up. even if I run WFO. Replace the plug, and it runs fine. It doesnt do this as often if I give the bike a easy cool down lap before shutting it off. I'm running one range hotter plug, and I've tried different ranges and brands of plugs.
Any Ideas ??
Thanks

YZThumper · Sep 15, 2002

I've seen several bikes do this and it typically indicates the the mixture needs more air. Try opening up the air screw. If you go more than 2 1/2 turns out, then get a smaller pilot jet. If the air screw and pilot jet doesn't clear this issue, then try to drop the needle one position.

A buddy of mine owned a YZ 250 that cold fouled plugs religiously. He tried every combination of jetting and fuel mixtures to no avail. The solution in the end was a different slide that allowed more air. If all else fails you might consider a new slide that allows more air. Some guys actually file their current slide to get the same effect, because new slides can be very expensive.

Good luck and let us know what you try and how it worked.

awilson40 · Sep 15, 2002

I was thinking the same thing, I just hate to go too lean.
I will pop in a leaner pilot next ride and see how it goes.

spark plug problem

awilson40

YZThumper

awilson40

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