Sounds like you're running lean and soft seizing. Have you replaced your crank seals? I betcha didn't....
Replace seals, Put in a fatter jet, or better yet get a bigger carb. Personally I tried the stock carb...no thanks.
To cool it down cheap, there's not many options,
The hpi cdi would do wonders, but it's $300.
A water cooled head would be great, but you have to find one.
Most people run a Wc kit instead of just the head. But that's$$$.
Check out my cheap ass fan cooling mod. It works wonders but it won't help you if you have airleaks or are under jetted...