a few months back i rebuilt my 250x engine. i put in a piston/cylinder kit from a guy on ebay that was already bored out into it. it was having trouble ideling and hard to start and i noticed it was easy to kick over so compression right? i pulled the engine apart and notice that about half a cm. ring on the top of the cylinder had carbon on it like the piston was not going all the way up. is that right? i know the 300ex has a longer stroke but i compared the piston to my old one and its the same. are the cylinder heads diffrent lengths? i dont have the old one here with me to compare.