took my boat out yesterday ran fine for for 10 minutes then started to surge/hunt on and off at 3 second intervals by about 300rpm @ 2500rpm , increasing throttle fault cleared.later at planing speed 3/4 throttle boat would start to hold back,would clear with full throttle,engine did not stall if returned to idle.at end of day would only rev up to 3000 rpm but would hesitate and when at full throttle deep air induction noise heard.also a separate fault had intermitant misfire at 1200rpm for few seconds and then cleared .engine has new plugs fitted new fuel lines and primer bulb+filters carb cleaned,engine is running on 50:1 premix oil pump pipe blanked off on VRO.and has round black 3 wire plug next to large red loom plug disconected.is this the correct thing to be done when running on pre mix to stop buzzer,no buzzer sounded,but buzzer only gives a weak sound when ignition put on.was watching water pee hole and always had water comming from it.tank vent was open,could it be a weak pump? 