Have an 04 crf50. It's 4th 50 I have owned. This one won't pull hard, just falls flat and is about 5 mph slower than my other bikes. Stock gearing. I have played with the needle and the main. Bike runs good, no bog and feels like it is jetted right. Don't know if this is just a sign that it is time to change the rings, or a valve seat issue. It smokes a little when cold.....but it is 35 degrees in Cleveland. Anyone ever have there bike lose power at the top?

 

Could be alot of stuff. It would be easy to try a compresion check. I think you can get a tester at auto zone. Then return it when your done!!

 

if cold its prob just from i bein cold alota bikes do that till warm.