i have a 1992 kdx250 and when i ride black crap shoots out of the silencer and all over my swing arm. i run 50to1 through it with 93 octane and race oil from a local shop but the kid i bought it off of (i bought it about 3 monthes ago) beat the crap out of it and i was wondering if that had anything to do with it. i think its the jetting , but im not sure. its torn apart right now and i was wondering (if the jets are the problem) what size i should get.