I´ve got the same type of problem. I can high rev it up to the top of 2nd, (about 85kph) then in third it only goes up to about 7500 rpms and sticks around 90-100kph. Fourth revs to 5500 rpms and stays at the same speed. Feels like a governor, but I don´t know what´s causing it. I did a carbjob, checked my fuel valve for rust from the tank or debris, tightened my air intakes at the carb and nothing is presenting itself as the problem. HELP!