80hp Merc Outboard - 60% power at WOT

[zif0684]

I just picked up a 1980 3 cylinder oil injected 80 hp merc outboard. I've had it out 4 times and each time is has done the exact same thing.

I will let the motor warm up a few minutes idling, once underway it will power up just fine but only to about 60% power even at WOT. A few times while at WOT it jumps like it momentarily jolts to life but it is short lived and it returns to running at around 60%. After running for about 10-15 mins I can shut it down, let it sit for a few minutes and the next time I start it, it runs like a top with full power for the rest of the day.

After the third trip out, I went through the carbs which were in good shape to begin with but the issue still exists. From what I have read, it could be an ignition problem - perhaps low/no spark on one of the cylinders? I don't understand how or why it just corrects itself after running for a while and what kind of issue that might suggest. If it is an electrical issue, I'm not sure where to start.

I should mention that the motor smokes a decent amount on start up and while first running at limited power until the power problem clears up - perhaps a hint that one of the cylinders isn't firing and thus why the extra oil is burning off?

 

[quicktach]

Start by looking at your plugs - change if need be. Check your spark with a tester -- good purple flash? Check all wiring for cracks, dirt accumulation, loose connections, any signs of burning or overheating on electrical components, clean and tight grounds.....no sticking advance mechanism...

 

[Chris1956]

Gee, a 1980 80HP Merc would have 4 cylinders, I would think. You might verify by serial number, exactly what you have.

 

[zif0684]

Gee, a 1980 80HP Merc would have 4 cylinders, I would think. You might verify by serial number, exactly what you have.

You're right, it's a 1987. The last owner was sure it was a 1980.

I've replaced the plugs already.

 

[Chris1956]

That is a tricky one. A couple of suggestions: Check for a leaky fuel pump gasket. Maybe the fuel pump gasket leaks until the motor is warm. It is a WAG.

When she is running poorly, pull the spark plugs and see if one is fouling. Maybe the float in a carb sticks for a while, for some reason. It has happened....

 

[zif0684]

RESOLVED - I had a corroded wire coming from the stator, once repaired the problem was resolved.

However, I have since developed a new issue. This one is fuel related.

While trolling at slow speeds the motor likes to stall; each time is stalls I notice the ball in the fuel line is soft and needs to be pumped/firmed up. It only happens at low RPM. Once past 25% throttle it runs fine.

I suspect one of 2 causes. 1 - I have a leaky carb from when I had them off to clean while trying to resolve the previous issue (would a leaking carb cause the fuel system to lose enough pressure while moving at low RPM)? , or 2 - could it be a problem with my fuel pump (it seems like it's not sucking gas hard enough to keep a steady pressure on the fuel system).

 

[Chris1956]

It could also be a small air leak into the fuel line. Small enough that it only affects idle and slow speed.