Lazy Yamaha 8HP

[Hardley]

Lazy Yamaha 8HP

MY outboard will run at full revs out of gear, but when I put it in gear it will only run at quarter revs, any more and the engine dies.
Have sprayed Carb Cleaner in the air intake, but no improvement.
Any suggestions regarding what is going on greatly appreciated.

 

[VicS]

Lazy Yamaha 8HP
MY outboard will run at full revs out of gear, but when I put it in gear it will only run at quarter revs, any more and the engine dies.
Have sprayed Carb Cleaner in the air intake, but no improvement.
Any suggestions regarding what is going on greatly appreciated.

2 stroke ? 4 stroke ? Age?

Checked, cleaned, reset, or preferably replaced plugs?

Good sparks on both cylinders? ......... could be be running on one cylinder only.

Checked fuel supply? filter?

Does closing the choke help? If so it indicates a dirty carb

Remote tank presumably? Does pumping the bulb help? if so could be faulty fuel pump or air ingress into fuel line

Spraying carb cleaner in air intake will do nothing.
If the carb is dirty it has to be dismantled and all the jets and passages cleaned. Rebuild with carb kit.

My money will be on a dirty main jet in the carb if the plugs and sparks are OK

 

[Hardley]

Thanks for your reply, it is a 2 stroke engine, old but normally very reliable.
Serviced with new plugs every year by Yamaha agent.
Filter replaced this week.
Will check other points raised on next visit to boat.

 

[ctva]

...My money will be on a dirty main jet in the carb if the plugs and sparks are OK

That would be my first thought. If it's a 2 stroke, the carbs are quite easy to clean.

http://www.boats.net/parts/search/Yamaha/Outboard/1994/8MSHS/CARBURETOR/parts.html
Check the serial number abut this site is great for service info.