01 CR250 surging problem

[Wavfact]

I'm going nuts over this surgung problem I have.. When the bike is cold, it runs fine, but once it wams up I get surging.. I've taken the top end off, had the cylinder & head resurfaced, put back on using copper spray gasket sealer and torgued to specs. I took the pipe off, put new O'Rings in it and put some exhaust silicone gasket sealer on it, then allow to cure for 24 hours.. I just put a brand new carb on this bike (the JD Jetting kit pre-installed in a PWK Airstryker). Replaced the reeds.. Put a new intake gasket on (again using the copper spray) and even put silicone sealer on the carb boot (reed side) being careful not to put too much on. I still get surging! ARGH! Whats odd is, it only happens after the bike gets up to temp and only at low RPM's or idliing.. 1/8 to WOT, all is fine.. I've even retorqued the head..

Anyone have any ideas? I've heard it could be the iginition side crank seal, but there isn't any oil leaking in there, no change in RPM's when I pull the cover off either and no surging at higher RPM's..

Dennis

[ossagp]

you seldom get any leaking with a bad ignition side seal. try setting the bike to idle and loosening the ignition cover, if the idling increases in speed, the seal is bad. it may still be bad even if that test doesnt show anything conclusive. fyi i can get 7 years out of either side seal. it also may still be on the rich side down low.

weak stators sometimes produce funny results too. wish it was here.

[Wavfact]

I just took the flywheel off (out of frustration) and am waiting for the oil to drain, then I'll replace the seal just incase.. I did notice a tiny droplet of oil on the inside, behind the flywheel.. I'd think if it was surging like it has been that there would be more oil in there than a small spec..

Been chasing this surging for awhile now.. Spent a small fortune trying to cure it.. but I must admit, that new carb is awesome! I bought one for my RM250 as well, it now pulls the front end up in 1st, 2nd and 3rd gear! Has crazy power throughout the throttle range.. Instant throttle response with no hesitation, no bogging in the lower gears/RPM's anymore. Now you really have to hold on when nailing the throttle and take extreme care not to flip the bike. LOVE IT! the JD Jetting kit is great.. pulled the plug after 15 minutes, color was perfect..

Dennis

[ossagp]

The response is noticeable on everything I have changed over too.

[mirrors]

Please post what you find, when you find out what is wrong as I have the same problem in my 98 CR250.

I thought it might be the float level so after a hard run when it was surging away at idle I turned the fuel tap off. Took ages but eventually it started to idle smooth. Ran smooth for about two seconds then ran out of fuel.

Thought ahha, must be running too rich. Got it started again and screwed the mixture screw to the point of falling out and it didn't make much difference to the idle.

Seems strange to me. In all my other bikes, the mixture screw whould only have about one revolution (half in either direction) before it idles really rough. I have it out two turns like the books says and screw it in one and the idle goes bad but screw it out and it doesn't make much difference. Is this normal?

Is the surge in yours also noticable when cruising along at low speed with no load? Mine does.

[AV8R]

My 00 YZ250 does the same thing. I can say with great certanty that it has nothing to do with you seals. I just rebuilt the bottom and top of my YZ including new crank and seals and it still does it.
The closest I have come to solving it is to run the pilot screw slightly lean this seems to help but not eliminate the problem.
I have noticed that the Kien carb on this bike in not very sensitive to pilot screw adjustments and I can turn the screw quite a ways before seeing any difference. Where as the Mikuni carbs that I have messed with are very sensitive to air screw adjustment once you get close to getting it right.

Which carb did you switch over to? I might be interested in that mod.

My sons 00 CR250 with the same Kien carb also surges at Idle.

I did notice that it only surges for a about 10 seconds at idle after you have been running it hard then settles down. Is yours doing the same?

I would also be interested in finding a fix for this annoying trait. I have messed with the jetting plenty and that does not seem to fix it. My spark plug indicates a perfectly jetted bike, so I am at a loss also.