Bodido, thanks for the info, it was damn helpful.
I ask this because i have an OS 12 CV-X on the way that i scored for $65 US brand new...and was just curious...
At first its going in a 2wd buggy basher, but i am tooling with the idea of getting a XXX NT to race.
5 minutes on a tank

dang thats really worrying, is that anything to do with having to run it rich to keep it cool enough? I've heard that the stock square head doesnt cool the engine enough and must run rich.
How big was your tank?? 75cc?