Top End?

[ldub128]

Does anybody know if a top end going bad will cause a bike to not wanna idle when warm? Ive got a yz250 and it will idle fine while the engine is cold but as soon as it comes to temp it will die out. Ive got the idle control turned as far in as it will go and the bike still wont idle. Any help would be greatly appreciated. Thanks

 

[truckster225]

Sounds like a possible compression problem? Maybe try a compression test when the engine is cold, then again when its hot.

 

[brentn]

Sounds like a possible compression problem? Maybe try a compression test when the engine is cold, then again when its hot.

What kind of numbers should you be getting when it's hot/cold?

 

[truckster225]

Well it should always stay above 120psi. Cold and hot. If you test it when its hot and it drops to like around 90psi, it wouldn't stay running.

This may not be a problem, but its always best to rule out the easy things first.

 

[whenfoxforks-ruled]

Idle control? What year yz? The slide stop, air mixture screw or the choke adjuster?

 

[TRexRacing]

If the jetting is rich that will happen in hot weather.Start real easy when it's cold?Check that pilot jet.

 

[ldub128]

Its a 1990. I think its the idle screw. What is a slide stop? im confused.

 

[whenfoxforks-ruled]

There are 2 screws on the left side to adjust the carb. The top one is the slide stop, and the bottom one is the air screw. No idle adjustment, per say? If you have spun the top one all the way in, and can not achieve an acceptable idle, the slide/ slide stop screw may be worn out.