30hp yamaha problem

hi all,

im having an issue with my yamaha outboard. it will start and stay running but only when close to full throttle. as soon as i ease up on the throttle it cuts out. any idea what could be causing this?

thanks lads.
Tom

What type of Yamaha? Is it an older 2 stroke (self mix) or a newer 2 strok (Auto Mix) or 4 stroke?
First thoughts for me are towards the Carb. Perhaps a blocked low speed valve, if there is one on your carb.
If you haven't worked on an engine is great details before, the carb is not a good place to start.

Kev

Hi MAC

its a 2 stroke auto lube.

If your able, it would be worth stripping and cleaning the carbs if they have not been done in recent years. It's amazing how left over fuel will gum up and turn to varnish.

There is a bit of a cheating way to do this without fully disassembling the carb. Not as good as a full clean, but well worth a go.

Get some Quicksilver power tune. It's a specialized de-carb spray....
Note you are going to create huge plumes of while smoke so try this is an open area, if possible.
Basically with the engine running, the engine cover off and and carb cover off, spray a 2 or 3 small squirts into the carb. The engine will stutter and you will see the smoke. Once the smoke has cleared, spray the power tune in until it chokes the engine and it cuts out. It might struggle on so be prepared to stop it, just in case it wont die. You will be spraying about half the can in there. Remove the spark plugs and spray a small amount into each cylinder. Make sure you spark leads are not grounded and / or kill switch is active and rotate the flywheel to distribute the spray in the cylinders. Leave it overnight. The spray will breakdown all the crud / gum inside the carb and on the cylinder walls.

The next day start your engine some where away from people On the water is better. If on the water run the engine at WOT until the white smoke has cleared. If not on the water run it at above idle.... It will take a few minutes for all the crud to be burned off. It will look like your trying to contact the Indians. HUGE plumes of white smoke, much worse that when you sprayed it into the carb.

After the white smoke has cleared, change / clean your spark plugs. They will be badly fouled.

I have managed to bring a 30 year old Johnson Seahorse 2hp engine and 2 old lawnmowers back to life with this spray.

Kev

Hi Mac,

thanks for that advise, if all else fails i will give it a go.

cheers, Tom.

Ok< got it sorted. there was a little water in the carb and a wire had to be sauldered as it was only running on 2 cylinders. took it for a quick run last night and it ran great.

thanks for the advice lads.

Good to hear!