Temporary Lousy Running

HELP. Been checking out the post for over an hour now and cannot find a similar problem. My 2002 Wr426 with 2000 miles (airbox lid removed, two step leaner jet needle, #158 main, 1/2 turn in pilot screw, stock muffler baffle removed, and grey wire still connected) will sometimes run terrible, I am talking backfiring, bogging when I open the throttle, poor starting, not accepting full throttle, etc. It seems to happen for about 10 minutes then it runs like a champ!!! It happens at different altitudes (I ride from 4,000-10,000 ft) and different times (on a cold engine and after a long ride). I've cleaned the carb several times. An Item of note is the CDI unit was replaced under warrenty about 1.5 years ago when my WR wouldn't accept anything above 1/4 throttle (that was a long ride home) and it ran so hot it browned the muffler and boiled the overflow tank. I'd ride it for three minutes and let it cool for 10 minutes. Since the CDI replacement no more overheating, but this temporary poor running has started. Any help you all can give would be greatly appreciated. Thanks!

Check the grounds, could be an intermittent open or something....

I've had the same problems (on another bike) related to the carb. I'd get serious power loss for a time and then shut down completely. I'd clean the carb and no more problems... for a while. Perhaps your fuel line/ petcock is getting clogged? Try cleaning your carb, tank and supply lines.

Just a bump here. I have the same bike, same year, same problem but not at high altitudes.

I had the same problem with my 01 WR for a while. Never figured out what it was. Would cough, sputter and backfire for a few minutes after I started it, then clear up and run great. I cleaned the carb several times and re-jetted. Funny thing was it would do it sporadically. :cry:

Have had no problems since putting in the YZ450 auto-deco cam. Not to mention that's the best mod I've done to my bike. :cry:

I can't help but will add a bump, I have the exact same bike and problem.

Try a new spark plug. :cry: Richen the jetting slightly as well. Go to a 165 main and raise the needle one clip. larger starter jet helps cold starting.

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