WHY??

 

check your idle ****. turn it so that the rpm's drop to where they're supposed to be. if they don't drop follow that cable up to the carb to see if there is something jammed up there. also check your throttle cables. they might be routed wrong or are hung up somewhere.

 

What he said. Cable routing is a common cause of a runaway engine. Air leaks can do it too. What all have you done to the bike so far? At least, what carb or fuel tank work? That'll get you on the right track.

Bill Dragoo
Norman, Oklahoma