Thought I would run this across everyone before I tear into the engine. 2004 450R been raced 2 raced without a major problem. My last race of the season 1 months ago it started to sputter(pop) a little bit through the whole RPM range. I thought that maybe it was bad gas. I put the bike away. Just got it out again, drained the gas, put fresh in and it will not start at all. Replaced the spark plug. No start. Tried to pull start it behind a quad and it wouldn't even try. I get varied opinions here, but two possibilities to me would be either a valve problem or a timing problem. Has this similiar thing happened to anyone here. I had another 450r that had a stretched valve that was hard to start, but it would eventually start. I can't get this bike to even pop once. Any opinions would be helpfull.