Nissan outboard runs only at half throttle and above

[chrisjholt]

1982 Nissan Outboard. 8hp 2 stroke. The motor was running perfect and then all the sudden died. No changes to any adjustments were made. Was motoring at about half throttle when motor suddenly died. I am able to restart with full choke and some throttle then runs but will not run lower than half throttle on its own. Runs better when I cover air intake half to 3/4 of the way. It's never had these symptoms before.

What I have tried. New plugs with spark. Compression is good by thumb test. Fuel is new. Oil is the best kind. New tank. New fuel line with good connections.

Cleaned the carb. Soak in cleaner. The reed valves look good. No obvious blockage or malfunction.

Does anyone have any suggestions?

 

[Sea Rider]

Re: Nissan outboard runs only at half throttle and above

Check gas pump diaphragms for wear, deformed, ballooned, if found defective, replace. Or carb probably was not well cleaned ?

Happy Boating

 

[airboat86]

Re: Nissan outboard runs only at half throttle and above

I dealt with this with a 1987 Johnson Sailmaster. It turned out the cylinders were so worn, the motor could not create enough vacuum to run at low speed. Check your cylinders my compression was 150 PS I.

 

[chrisjholt]

Re: Nissan outboard runs only at half throttle and above

Ok Thanks. I'll take a closer look at the diaphragms. I will also re-clean the carb.

 

[chrisjholt]

Re: Nissan outboard runs only at half throttle and above

That would be a real bummer if the cylinders are worn and its not getting enough psi. Did your motor suddenly die as well and then have the same symptoms?

 

[pvanv]

Re: Nissan outboard runs only at half throttle and above

Sounds like insufficient fuel delivery. Check/clean carb, verify pump, check fuel lines from tank to pump.

 

[airboat86]

Re: Nissan outboard runs only at half throttle and above

I had the very same symptoms. The motor would run in a tank with a test prop for two hours without stalling. When out on the water, it would run great at high speed and after throttle down would run for a few minutes and die. Went through the fuel system and after all was cleaned and rebuilt the problem persisted. The high compression was due to carbon fouling at the head and betrayed finding the worn cylinders. This is rare, but does happen. If the fuel system maintenance doesn't fix it, look at your cylinders.