idle problem

A 2 stroke...

They aren't designed to idle. Idling is for bikes that are less than easy to start.

Why on earth would you need it to idle more than a second anyway?

When you're riding it, you should be in the powerband, if not you're not doing it right.

mine dont idle too but it need to be adjusted, just turn the idle screw on the carb so it can idle(i dont know for a cr250).
On my manual, it say to set the screw to the lowest idle possible when the engine is at normal temperature(warm).. so it should idle.

idle is not needed to ride/race, but on a stop or on trail while waiting friend that are far behind or to smoke its usefull to let it idle in some case instead to hold the throttle or kickstart again.