2004 YZ250f

[JRude]

My son was riding this past weekend. The bike started bogging at just past 1/4 throttle. I checked the timing and it was off. I removed the the head cover and readjusted the the timing. The bike started and ran fine. He rode the bike for two laps and it once again started bogging at 1/4 throttle. Checked timing and once again out of time. What can cause I bike to jump out of time. Worn cam shaft sproket or possibly broken cam chain tensioner. I have just recently replaced valves,springs new piston and cyclinder and crankshaft assembly. I had checked valve clearance and they were good. Thanks for any suggestions.

 

[Rich Rohrich]

The lower cam gear on the end of the crank tends to be the most common cause of this on the YZF250s. Pull the ignition side cover and the flywheel and check the guide rail and the cam gear for excessive wear.

 

[stevena198301]

I'd say the auto cam tensioner, if it isn't the gear...