I built from scratch an av10 with new case, new crank, doppler 50cc kit, doppler o-ring head, $220 doppler pipe, CDI electrics and alot of time. This was a very spendy project. I am not real happy with the bike at this point because it takes a bit to get it into the rpm range where the pipe and porting turn on. And excess heat is becoming a problem. The next thing I am facing is at 50+ mph my tires, brakes, and suspension are not good enough to handle the roads near my house.
If I were to do it over I would get a 70 or 74cc kit that does not need to spin up over 8500 rpm to get some horse power. For me 40 to 45mph is fast enough on my little Moby.