I hope someone can give me some insite... I have an 05 YFZ450 which has stopped running on me and I can't seem to figure it out.
Bike turns over (piston goes up and down), plenty of spark, appears to be getting fuel, took air filter off to assure its getting plenty of air. Here is where it gets interesting... with the bike off, when I put it into gear and pull the clutch in the bike will not roll. Any ideas? Could it be a clutch problem? Timing problem? (I have pulled the valve cover off and the valves, cams, and chain all look ok).

 

get on yfzcentral and see if anyone can help you.