CR250 with a strange behavior

Jul 12, 2000
My –97 CR250 has this strange thing going on when the engine is warmed up. Sometimes when I let of the gas the RPM still hanging on a little bit above idlee, it’s enough to resulting in a gyro effect that rise the front when i’m in the air. It doesn’t always happens when I shut the throttle, but often enough to be realy enoying... Other than that the engine runs great, doesn’t bog or hesitate and pulling strong all the way.

Things I have done to try to fix this:
-cleaning the carb, twice...
-checked if the carburator vent hoses where clogged.
-spraying contact cleaner at the carburator, reed valve, crankcase and cylinder with the engine running to find any air leaks. ( but not under the magneto cover)
-checked the throttle grip and wire.
-cleaned out the exhaust port.
-decarbonazed the pipe and silencer.
-clenead the airfilter
-diffrent air-screw settings.

I haven’t checked the sparkplug yet... or try to set the idle adjustment to zero, I heard that on the Kehin PJ carb it’s better to just ignore any idlee...

The engine also has a new piston and rings and the former owner changed som bearings in the engine ( at a shop) so i guess most of the seals are new.

The only thing I have noticed is that there a two tiny little cracks att the beginning of the pipe, it doesn’t smoke but leaves some black oil marks, and I havent checked the conditions of the o-ring attached on the end of the pipe where its connected to the engine. Could this be the problem (hard to belive that)

One more thing. The jetting seems to be a little rich – main 190, pilot 62 (original 175 and 55) maybe there’s been an aftermarket pipe on it. But as I wrote earlier - it’s running pretty nice, and I mostly ride on a very soft and difficult sandtrack.

So whats the verdict, do I have to split the engine and check the crankcase seal? What is the best way to see if this seal is broken?

Thanks in advance
Jan 7, 2001
I'd go get an ignition side crank seal and put it in. This can be done easily by just removing the fly wheel and stator plate. The seal pops out from the outside but you'll probably destroy it with a screw driver in doing it. I usually put a thin coat of yamabond on the new one just to be sure. Tap the new seal in with a deep well 12 point socket.

While your at it check the cylinder base nuts and the bolts on the reed block. Actually just go ahead and put a new gasket in there too, it's too easy and cheap not to try.