80 HP Motor stalls when power applied

[bigiron]

My 1979 Merc 80 HP will start OK. Choke usually required. Idle seems a little rough but functional. When I ease it in gear it takes it but sometimes idle speed has to be increased to avoid dieing. When power is applied engine dies. If I choke it I can usually get it up to speed. <br />Engine runs fine when boat is on plane but as soon as I lower speed (as no wake zone) it dies completely. Engine will not run at lower speeds.It starts right up but when power is applied it dies.<br />Thanks.

 

[bigiron]

Re: 80 HP Motor stalls when power applied

Sorry, I did not mention that the carbs were rebuilt last year

 

[Chris1956]

Re: 80 HP Motor stalls when power applied

Bigiron, If the carbs were rebuilt, I will assume they are clean. If the motor has balanced compression, it should be easy to adjust the carb idle mixture. Your motor seems to be set too lean to accelerate. You need to open the idle screw on the top carb 1/8 of a turn and try to accelerate. If it accelerates smoothly, your done. If not, open the idle adjustment screw on the bottom carb 1/8 turn, and retry acceleration test. If motor doesn't accelerate smoothly, repeat the sequence. If you cannot get a reasonable idle(~1200rpm) and smooth acceleration<br />it is likely that you have a timing, spark or compression problem.

 

[bigiron]

Re: 80 HP Motor stalls when power applied

Thanks Chris1956. I will try that at earliest opportunity.

 

[bigiron]

Re: 80 HP Motor stalls when power applied

Would you believe the major problem was the gas hose. Replaced hose and things got better.

 

[Hickpoppy]

Re: 80 HP Motor stalls when power applied

I had a similar experience:<br />I trailered my boat up to Keuka Lake (Finger Lake) in NY and the motor started but was running very rough and would keep stalling. Finally, I got it to idle and revved the motor back and forth between 1k and 3k. WHen I put it in gear, it would go smoothly at WOT for a second or two and then seem to run out of fuel. I was at wits end, so I took the fuel hose and primer bulb off of my 9.9hp merc and the 60hp merc ran great. Could the Fuel hose really have caused this? Why?

 

[Elmer Fudge]

Re: 80 HP Motor stalls when power applied

air was probably getting sucked into the fuel line

 

[bigiron]

Re: 80 HP Motor stalls when power applied

One other question please. The boat comes up to speed very well and runs along at 25MPH very well. However if I cut the speed much below that it will run along for a while and then fall off speed and the boat will settle instead of planing.<br />There seems to be a subtle little area where the boat will really scoot and then it slows down. Adding throttle brings her up nicely but I don't really want to run at 25MPH when in a bit rougher water. It is a tri-hull and the faster speeds with rougher water beats everyone up.<br />Thanks