So the bike runs great when it is cold starts right up and I can run it hard for about 15 to 20 min then it starts to loose power and bog down until it eventually stops and the motor will die and you can’t start it until it cools down I was thinking that it might be a compression issue so I rebuilt the top end new plug piston and seals but that didn’t fix it any advice will be appreciated

 

Welcome to the forums.

What's your compression since the rebuild?

 

I don’t currently have a way to check it,trying to find a gauge

 

What was the compression b4 your rebuild? Extreme lean conditions can also cuase overheating

 

so After the rebuild compression is 110 psi

 

Compression is good. Do a plug chop and check to see if you're lean, as Kymco 450i suggested.

Didn't do anything with the flywheel, did you?

 

Didn’t do anything to the flywheel and what would cause it to lean out after it gets hot the carb isn’t dumping anything out and it runs great with good throttle response when it is cold

 

Sounds like carb might not be adjusted/jetted correctly. I have seen ignition systems work well when cold then beeak down under heat. If spark gets weak after warming up will cause an issue.
You need to thoroughly test to see what is wrong, or you can keep guessing and throwing money at it...