MERC120HP BLACK EXHAUST

[ENFORCER150HP]

I'VE JUST RECENTLY REPLACED THE MANIFOLD GASKETS ON MY 76 120HP MERCUISER 4 CYL. I WAS TAKING IN AIR. EVER SINCE MY ENGINE HAS BEEN BLOWING BLACK SMOKE. IT STANDS IN WATER AND GETS SO BAD THAT IT LEAVES A RING AROUND THE BOAT WHEN SITTING IDLE IN THE LAKE. I ALSO HAVE A FLAT SPOT WHEN TRYING TO POWER UP TO SPEED. OTHER THAN THAT IT IDLES OK AND RUNS AT TOP SPEED OK. PLEASE HELP IF ALL POSSIBLE. I AM STRANDED ON LAND WITH MY BOAT RUNNING LIKE THIS.

 

[McKenzie]

Re: MERC120HP BLACK EXHAUST

Is the flat spot only when quickly accelerating? What happens if you slowly give it throttle? If it only happens upon quick acceleration, it is most likely a problem with the accelerator pump. If you press down the pump arm with your thumb when the engine is off, it should feel nice and stiff, not soft. When you do this, a nice stream of gas should shoot into the carb barrels. If not, your carb needs a rebuild.

 

[flashback]

Re: MERC120HP BLACK EXHAUST

black smoke is unburned gas, adjust,rebuild,replace the carb .......good luck

 

[Dunaruna]

Re: MERC120HP BLACK EXHAUST

What flashback said. You have just repaired an air leak, the motor will automatically run richer. Look to carby adjustment or repair.