Re: are they 80cc
It's just a matter of getting them balanced right, and building a decent pipe, one of my '66/68.5' cc motors happily does over 9000 RPM. Lacks a little low down with a 36t, but flies.
The other one I'm still playing with, starts to ping up there, but will still do 9.
But I admit if there not balanced right, they start losing bits to vibration if you try and over rev them, I've heard the 48's tend to run a lot smoother.