Mercury 80 HP outboard

[Kissdude]

I was wondering if anyone could tell me why in my driveway my motor runs nice in forward and reverse but when I try to leave the dock it will die in either forward or reverse. I have a quick silver metal can for the test in driveway but changed it to a new looking one that I had. Do these lose suction or something? Thanks in advance!

 

[Chris1956]

No, the difference is backpressure on the exhaust. In the driveway there is no backpressure. In the water there is some backpressure.

What is your idle speed? Have you made any changes or repairs to timing or carbs?

 

[Kissdude]

I haven’t made any changes and I don’t know what idle speed is, been trying to find it in the manual.

 

[Kissdude]

Will I have back pressure using a test tank?

 

[racerone]

Open low speed mixture screws 1/8th turn at a time.----Test / repeat as needed.----Often makes the bogging go away.

 

[Chris1956]

I will assume that is a Merc from the late 70s or early 80s. They really liked a precise 50::1 gas:il mix. When tuned properly, they will idle OK on that. However, it does not take much in tuning or fuel mix to make a lousy idle.
My advice is to mix a fresh 50::1 fuel source and run it on the water. Motor warm, in set the idle mixture screws to 1-1/2 turns open. She should run OK. Now try to accelerate. If she bogs or stalls open the top carb mixture screw 1/8 turn. Try to accelerate. Again, if she bogs open the bottom mixture screw 1/8 turn. Repeat the sequence until she rund OK at idle and good at high speed.

 

[Kissdude]

Yeah its a 1979 80 hp. will I be able to do these settings with motor in a big bucket instead of muffs? The only change that I made was take an empty newer fuel can with me and , filled it with fresh gas on the trip out but added oil when it was full. It ran really good in each gear before the trip using the older can.