My buddy has a 05 yamaha 450, bought it new in 05. Has alot of hours on it, with no valve job. Within the pas month he has been having problems, it will run perfect for 2 hours or so and the start breaking up and die?? He thinks it needs a valve job which I'm sure it does. But that just dosent sound like that would be a symptom of valves?? Am I wrong?? Any insight would be appreciated.

nobody huh??

Could be a few things.

To much heat from lean jetting, to rich and causing the A/F to go to rich after it heats up, lack of oil, maybe a crank bearing is starting to show signs of failing.

I however do not think it is because of it needing a valve job. If that were the case I would expect to see signs of hard starting or no starts, low compression and bad performance.

Yea, hes gonna tear it down, but a local shop seems to think the stator is going bad...

Possible it could be the stator.

I've seen a 06 with a bad cdi, and his other 04 would break up... wouldn't die though and that stator was bad.

Yea his breaks up and dies and wont start for a while. But the battery seems to stay charged... So its workin for a while and crappin when it heats up I guess.