1982 merc 80hp stall when underload

[markgillbee]

Hey guys,
I have an 80hp 1982 Merc 2 stroke straight 4 outboard (very clean).
The issue I am having is that when I put in the water and put it in gear it stalls, although I can rev out of water in gear and it goes hard prop spins and seems very responsive.

The problem first started when I had the boat towing someone, motor was running fine then we slowed down ( kept motor in idle) and went to take off again flat stick and the motor just surged and stalled out.

We have replaced the spark plugs and turned the idle up but didn't seem to make any difference. some people are saying reed blockers, tune or even a contaminated fuel line.

If anyone could shed some light on my issue ide much appreciate any input. Many thanks.

 

[CharlieB]

Re: 1982 merc 80hp stall when underload

Generally an engine that idles/revs fine on the hose but will not once in the water is a sign of inadequate fuel supply, lean idle mixture, dirty carbs, possibly a small amount of water in the carb(s).

However, you cannot rule out an ignition failure on one cyl, test spark on each to be sure ignition is functioning correctly. While you have the spark plugs out it never hurts to verify compression is fine on each cyl.

Once spark and compression is verified then since this was a sudden onset of symptoms, I would lean towards water contamination of the fuel.

Install a water separating fuel filter, change the filter if already installed.

Pull the float bowl drain plugs ONE AT A TIME, pump the primer bulb while each plug is out, flushing anything out of the float bowl. Have the motor well level.

Test fuel pump output by pulling the fuel line, point it into a suitable container, pull the lanyard so you do not start the engine, crank and observe the fuel output to ensure ou have a strong pulsed stream.

Reassemble and retest on the water.

If performance is not restored then it is time to properly clean and adjust carbs.

 

[markgillbee]

Re: 1982 merc 80hp stall when underload

Thanks alot mate for the info it is very much appreciated ill will try what you have recommended, cheers