yamaha 2hp 2-stroke idles fine but dies at higher revs

[janul15]

Hello. I just bought a used Yamaha 2hp 2-stroke engine. Took it out and it idles fine, but dies when I try and increase speed. Starts up again after a few minutes, then the same thing.
Checked the spark plug once and it was wet and black. Using 50:1 fuel oil mix as the previous owner recommended.

 

[mike_i]

Check the fuel filter. What condition is the primer bulb in? Was it compressed or normal? Try pumping it when the motor starts to die. What's the level of gas in the tank? Does the motor die as the boat gets on plane? Loosen the gas cap and try it.

 

[janul15]

Thanks, mike-i. I didn't find a fuel filter, or a primer bulb. The engine dies as soon as I increase the throttle. Gas cap has been loosened. I should change the fuel tap (on/off) directly under the tank. (It's very old, very stiff to move, but I don't know if this could cause the problem)
Richard

 

[janul15]

I've just looked at a replacement fuel tap, and I'm thinking maybe a filter is incorporated in the assembly. How should I clean up the assembly, before splashing out on a replacement?

 

[airshot]

I think I have the same motor but badged as a Mercury. Sounds like fuel flow issue from the tank. Probably in the fuel shut off valve. Disconnect from carb and see how good the fuel flow is!!! While you have it apart, cleanout the fuel tank, replace the hoses, mabey even flush out the carb, easy to work on these little motors.
Will bet a good thorough cleaning of the fuel delivery system will get you going.

 

[janul15]

Thanks all. Yes, fuel delivery was the problem. Took the fuel tap/filter off sprayed sea foam into it, then soaked in washing up liquid, then soaked in clean fuel, then sprayed again with sea foam. Problem solved. Does anybody know a good setting for the air/fuel mix control. (how many turns out from fully seated)? If nobody knows, I'll leave it as it is.

 

[airshot]

If the engine is running, then adjust until it runs its best. If motor is not staying running, they typically start about 1 1/2 - 2 turns out as a starting point