speedfight variator not working WHY?

I've just bought a speedfight 2 it was a non runner i've now got it running,but the variator does not seem to work i've stripped it checked it its had new rollers(already in it) don't know what weight i've took out the washer/plate it has a leo vince zx exhaust fitted and runs spot on but only does about 25mph revvving its arse off also the set off is terribble as though its in to high off gear(if it had gears)
i've had it running with the cover off when you rev it the variator does not change.
any body got any ideas whats wrong?