I have a 1997 KX250 that keeps fouling the spark plug after about 4 hours of riding, it always starts first kick with a fresh plug when its cold and warm. it doesnt hesitate when im riding and always idles fine, i mix a 50:1 Mix. Any help apreciated, Cheers.
First guess would be jetting of course.. If you ride it in the upper RPMs most of the time, go with a leaner main, if you're more of a woods mid RPM rider, go with a leaner pilot and see what happens from there..
I've also had compression problems that have caused fouling plugs (Blown crank seal w/ stuck open power valves), but mess with the jetting first.
How old is the fuel in the tank. In Oz we have really **** fuel. Since we've gone unleaded I find the oil separtes from the fuel the older it gets and can cause fouling plugs. Use fresh fuel. Check the jetting as stated in the previous post. Another one is see if its a bit smoky when you start it as you could have a leaking crank seal whcih allows gearbox oil into the crank on the up stroke causing gerabox oil to be sent into the cylinder with the next charge. This can cause fouling and even worse.
split the cases and find out if the crank seal is leaking, it could be multiple things, like rnning to cold of a plug,jetting is off,gas mixture is old,to rich of a mixture,air filter element can be clogged,too much oil on the airfilter,crank seal is leaking,or your top-end can need to be re-built at least the rings
Im running the correct plug for the bike, the gas mixture is new, my air filter is new, and the compression seems fine when i kick it(not tested though). Im not experienced enough to split the cases so i will have to have it professionaly done, will it be expensive?
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