Help fault finding with CR250

[QuentinCR250]

Hi guys,

After a couple of hours ride other day during which the bike went fine I stopped for 5 mins before riding back to the car, on the trip back the bike coughed a few times just like the fuel tap was turned off even though the gas was still on, It was still rideable but ran rough, by the top of the hill it had mostly cleared and I thought I was back to normal.
On the next trip out I only got a couple of laps and the bike was running really rough, I suspected a carb problem so drained the bowl after this the bike ran even worse. I pulled the carb right off and opened it up but havn't found anything that looks out of the ordinary. I have checked the powervalve inspection hole and the valve is turning when the throttle is blipped, i also checked the reeds when I had the carb off and they looked fine.
On the last short test ride after having the bowl off, the bike ran smoother but seemed pretty gutless then half way through the lap it came right and was awesome for about 1 minute before losing power again.
Do you think this sounds like a carb problem? I have got it off at the moment and are going to give it a full strip down in the weekend. the bike is a 2001 CR250 which runs the Mikuni carb. Does anyone else have any other ideas I should check to eliminate any other possible problems? Thanks for any suggestions...

 

[christopher in tam]

Sounds like my RM when moisture gets under the flywheel cover. Were you riding in wet conditions, or do you use a pressure washer? If moisture is the problem (not sure but it could be) you will need to replace the plug after you get everything dried out... all it takes is a few miss fires on a 2 stroke to reduce a plugs performance.

With moisture under the flywheel cover it will run fine untill enough heat builds up under the cover to vaporize any water in there and then it will start acting up. Shut it down for 5 minutes and it will run fine again for 30 seconds before acting up again... and so on...

 

[DLHamblin]

Did you try a new spark plug yet??

 

[mxneagle]

I had a wire break where it entered the CDI box on my '97 CR250 and it behaved something like that. It looks like you've checked the carb out pretty well, now do some electrical investigation. Check your kill button (I've had it short sporatically before also), the ground coil ground, new plug, wires etc...

 

[bikepilot]

I'd try a new plug first off. If your old one is getting carbon fouled it can cause all sorts of odd problems. You can spray under the ignition cover with wd-40 to displace moisture.

I'd also spray out the main and pilot jets with carb cleaner and compressed air and set the float level. Additionally, there is a small fuel filter in the tank, attached to the petcock. This filter is known to clog if not cleaned from time to time.

good luck

 

[QuentinCR250]

Thanks alot guys thats awesome just what I was looking for... all options are worth eliminating. One thing which is interesting is that did have the flywheel cover off a ride or so ago for the first time, I also saw the seal was not 100 percent so it could be a strong possibility. At the time I was riding when it started playing up the track was dry and the bike went ok for about an hour, however I have ridden on alot of wet tracks recently and I do wash my bike with a bit too much pressure ocasionally. I think I will pull the cover off and WD40 or CRC it then leve it off for a week and replace the seal.
I did change the spark plug at the track, but unfortunatley I was only able to replace it with an already used plug, I know the used plug was ok last ride and was only changed as a routine maintenance thing, I will buy a new plug also.
Thanks bikepilot I didn't know there was a fuel filter I will drain what fuel is left in the tank, clean the tank and filter as well as giving the carb a going over with carb cleaner and compressed air since its off the bike.
Once again guys thanks alot for the time to reply as its given me a few more worthwhile ideas...

P.s will also check the kill switch and look over the wiring.... is it safe to give everything in the under the flywheel cover a good coating in CRC? :)