Engine only runs when Prime Start Assembly is removed...

[Goofynick6]

Ok,
Have a 20 HP Yamaha, which I think is around a 2006 (haven't looked). It will start sometimes and idle for 3 seconds and die. If you give it any amount of throttle, it dies instantly. I found that by removing the prime start assembly and plugging the hole with my thumb, it starts and runs very well. I noticed the prime starter did seem to be in a different position after unplugging it and waiting, so maybe it does work somewhat? As soon as I put it back in, the engine stalls right out.

Is this just needing a new one? Or is there something else and this is just a red herring?

Thanks,

Nick

[boscoe99]

What is the complete model of the motor?

What position is the over ride lever/knob in?

[99yam40]

Clean the carbs and prime start passages, adjust as manual calls for, and then test PS like the service manual says

Or maybe you have the red lever turned off

[rodbolt17]

it has to be a four stroke 20, they were the only 20hp yamahas to ever have prime start.
it also tells me the poster is following peter cottontail with out knowing where the trail leads.

clean the carb,fuel lines and fuel pump.
go play.
by REMOVING the primestarter it just went richer than the engineers imagination,bypassing all other carb circuits.

[Goofynick6]

Clean the carbs and prime start passages, adjust as manual calls for, and then test PS like the service manual says

Or maybe you have the red lever turned off

Not familiar with this lever. Where is it? What is its purpose?

[Goofynick6]

it has to be a four stroke 20, they were the only 20hp yamahas to ever have prime start.
it also tells me the poster is following peter cottontail with out knowing where the trail leads.

clean the carb,fuel lines and fuel pump.
go play.
by REMOVING the primestarter it just went richer than the engineers imagination,bypassing all other carb circuits.

Took pump apart, was clean as new, pumps fuel very well when it is being cranked over. Has only ever had non-ethanol fuel run through it.

[boscoe99]

I don't think an F20 has the over ride lever for Primestart.

Too bad folks won't tell us what they have when asking for help. Seems to be the modus operandi of the vast majority.

[Goofynick6]

I don't think an F20 has the over ride lever for Primestart.

Too bad folks won't tell us what they have when asking for help. Seems to be the modus operandi of the vast majority.

Sorry, it is my father in law's boat/motor and he has no clue how to fix a motor. I am a mechanic, but for cars, not so much outboards. I will have to go over to his house to get the model number.

Thanks,
Nick

[99yam40]

Make sure to get the serial # also.

Had no idea the F20 would not have the ability to switch prime start like all the others I have seen