40 hp yamaha question

[dtacmed]

I have a 40 hp yamaha 3 cyl. It idles good and runs good at full throttle. However it "chugs" when slowly advancing the throttle or at very slow speed. I have changed the plugs. Any suggestions.

 

[Forktail]

Re: 40 hp yamaha question

My Yamaha 40 (detuned to a 35) did the exact same thing, especially when cold.<br /><br />This motor has a thermostat. You may want to replace it to ensure that the motor is warming up. It helped for me.<br /><br />I also removed and completely cleaned my three carburetors. I readjusted and re-syncronized them. Problem solved. Great motor.