im going to check it out tommorow but this is what happened.........i tok the exhaust pipe off and lost the metal ring that goes in the head before you put on the exhaust again.... so just for a little while i put on some silicone sealant and it made a cracking sound coming out of the head when i started it or reved it when it was cold.???? wel now i puit the metal ring back on (got a new one) and its still doing the same thing...i cant figure it out....any help? or has this happened to anyone before? i have a tb 88cc bbk with race head and carb....tb manuel clutch and tb rev booster... any help? thanks.