alot of things can cause air leaks. broken boot on your intake side or reed side of your carb, top end not torqued right, top end gasket broken or missing... any gasket missing for that matter, reeds not seated right... an air leak would cause your bike to run lean which in turn will suck in too much air and blow your top end. i am not exactly sure what the science in all of it is, but now you know what i know.