2004 TE250 Runs fine until warmed up

My TE has a rough running problem. The first time it happened I thought it was running out of gas. It will start fine and run fine until it is thoroughly warmed up. Then it starts to sputter and surge like crazy. Even on a flat area it'll surge while I'm holding the throttle still (or trying to). It makes going up hills a real challenge because I never know if it will bog down or pull the front wheel...

The bike is stone stock. I've cleaned out the carb (off bike) twice and this always comes back. I'm thinking carb/jetting, but could this be an ignition problem?

Any help appreciated.

Does it have a fan?
Is it overheating?
My bike, when it overheats, it has symptoms similar to what you are describing.

I would replace the spark plug first thing.

No fan for 2004, but you bring up a valid point. I'll double check coolant level. I'm pretty sure the plug replacement has made no improvement.

Thanks for the reply.

Has it sat up for a time, did you clean the jets with a piece of copper wire? If the jets have a coating of build-up inside them, making them, essentially, a smaller size, the bike will run hotter.

Brad in StL Did you ever determine the issue?? My 2004 TE250 is experiencing the EXACT same issues. Carb has been cleaned several times, I even changed jetting and carb set up, new spark plug, good gas, etc.... nothing has solved it. I REALLY need some help on this one!!