250r shorting plugs

[Corkinman]

My 1984 atc 250r keeps fouling out the plug after about an hour of use? what do you suppose the problem could be?

[Corkinman]

also i am running 50:1 using mobil syn. so i am pretty sure its not the oil, and when it is running it runs like a top.

[Billy Golightly]

crank seal, improperly tuned carb, clogged airfilter, clogged exhaust silencer, bad reeds, bad headgasket.

[4cylinders]

hey, what color is the plug? If it's kinda gray metalic, you may be too lean, and the piston is transfering metal to the plug.