[SJ90]

Hi. I just bought a second hand 04 crf250r and when it starts it blows blue smoke like a two stroke for a little while. After it is warm it cleans up but it still smokes (blue) a little when I accelerate hard. Does anyone know if its the valves or more likely the piston and rings. Thanks for the help.

[woodsman]

I'd go with piston rings. If it starts easily, then it ain't your valves.

[SJ90]

Thanks!!! it starts first or second kick every time.

[SJ90]

Hey, I ripped the motor down last night and the piston and rings look fine, I had a Honda mechanic with me who agreed. The valve clearances are Left Intake=.127, Right Intake=.1143, Left Exhaust=.2159, and Right Exhaust=.254. There is oil on the piston but we checked the valves by putting gas on the back side and they didn't leak. Does anyone know why this thing blows so much blue while its cold?

[124]

Hey, I ripped the motor down last night and the piston and rings look fine, I had a Honda mechanic with me who agreed. The valve clearances are Left Intake=.127, Right Intake=.1143, Left Exhaust=.2159, and Right Exhaust=.254. There is oil on the piston but we checked the valves by putting gas on the back side and they didn't leak. Does anyone know why this thing blows so much blue while its cold?

What is your compression? Leak down %?
Other than catastrophic failure, I know of no other way to visually look at piston rings and say "piston and rings look fine."