I have an 89 Yamaha 50deto that idles fine and shoots out of the hole good, but the last little bit of throttle advancement it hesitates (around 4500 rpm), acts like it is bogging down and will not go any faster.
Have someone pump the fuel bulb when it starts to bog down at WOT and see if it picks up. The engine is probably running lean at max throttle. The question is whether it is a restriction in the tank/fuel line, bad fuel pump, or clogged main jet of the carb. If it picks up with hand pumping the fuel bulb it is probably the fuel pump.
Using a small seperate tank and fuel line to test with will help eliminate all but the fuel pump and carbs. Backing off the two bolts mounting the fuel pump and squeezing the bulb carefully and seeing if the pump leaks is an easy test for it.
I plan on cleaning the carbs soon, I just bought this motor and am not sure what's been maintained on it, I will try the fuel bulb trick first and see if that helps it, Thanks for the advice!
