Have a 1990 85 yamaha. After i put it into gear and throttle up, sometimes it thottles up, and sometimes nothing. It will just idle or stall. Replaced fuel filter, pump, rebuilt carborator, timing is ok.
It could be the cam adjustment on the accelerator or something more serious. Have you done a compression test? I had a similar problem with my 1990 50Hp which had to be rebuilt
