It may only be the oil pump needing adjusting.....when the throttle is opened full, then the oil pump delivery should be full too. If you have any doubts about this, remember you can run the scooter on a oil/petrol pre mix without any problems - about 25:1 ratio is about right. Two stroke oil pumps also need to be bled if they have been tampered with - there is a bleed screw on the side to assist with this.
John
June 2008