yamaha 40hp 1986 won;t run at wot

[mitjoh246]

I just purchased a used Yamaha 40hp 1986 with oil injection. Runs fine at idle and up to 3/4 throttle. When I run wide open the motor dies and can barely get back to dock. New gas tank,plugs, fuel hose,water separator. and clean and inspected carbs. Ran Mercs for years but I am stumped. Fuel pump?? Ignition ?? Any ideas ? Thanks

 

[Yamajoe]

Re: yamaha 40hp 1986 won;t run at wot

Check the link and sinc and timing, esp for WOT. when the problem occurs at 3/4 throttle, is the primer bulb firm or has it flattened out; is the air release valve on the tank open? check fuel lines and connectors - no leaks; have you got the correct fuel connector (arrow towards the motor); to check fuel pump, have at 3/4 throttle or more pump the primer, if the motor picks up, then you need pump overhaul; finally, your main jets make be full of crud, tear down the carb and ensure the jets are removed and orifices cleaned and use air.

 

[mitjoh246]

Re: yamaha 40hp 1986 won;t run at wot

Thanks for the reply. Triple checked all fuel connections and added water seperator. All new and functioning. Motor runs smooth at 3/4 throttle but immediatley dies when full throttle attempted. Will try pumping bulb at 3/4 throttle but supposedly a new fuel pump was installed just prior to my purchase. Once motors stalls, must wait a few minutes to restart and never runs smooth from that point. Strictly a weekendender with very rusty mechanical skills but difficult to get boat and motor to a certified tech. Thanks again though.

 

[mitjoh246]

Re: yamaha 40hp 1986 won;t run at wot

Forgot to mention vent is open on fuel tank and primer bulb remains firm when problem occurs.