i have a ltr450 that i just put new crank,piston rings ,new cylinder. the reason i did is that the piston broke and droped my valves.ok now when you time it the t'and alighen the cams in time.won't start backfired a few times.took the plug out to make sure that it was topdead center and the piston is down a little bit from topwould this be because my magneto key is bad. need help would like to ride it soon.what could be my problem.