There is a post by markus that has my exact problem an he posted he fixed it without saying how. It has low power when taking off until about 3000 rpm and when turning left,even a very slight left, if you hold it there it will eventually bog down(without misfiring) to 2-3000 rpm. Turn the handlebar back straight and about 3seconds later it will take off normal. It is definitely fuel,exhaust blockage, or air restriction because it is not misfiring it is bogging. Tank is full, tank is clean, filter is new. Rave valves??? Is this possible?