What all can cause fouling?

[chuey_316]

I have a chance to pick up a really nice Blaster today. The owner said that it has no low-end torque and keeps fouling plugs. My first thought is jetting or carb settings, but what else could cause that? Gaskets, crank seals, reeds, or pretty much only the carb?

I should add that has an FMF pipe, shorty silencer, board .30 over, and a ported head.

It's either this bike, or a really nice 250X, with a 350X engine that the owner says needs a new crank for the same price.

 

[Larry's Shee]

Wrong plug, wrong oil mix, maybe mixing fuel and has oil injection, bad crank seal sucking trans oil. Way dirty air filter, plugged exhaust.
No matter what, change the crank seals when you get it. They are 12-29 years old.