WHY DOES MY 1976 70HP JOHNSON DRIP BLACK OIL OUT THE PROP AFTER I RUN HER ALL DAY?
IT IS NOT LOWER UNIT OIL. THAT CHECKS OUT FINE. I AM MIXING 6 GAL GAS TO 16 OZS. OIL TCW-3. SHE ALSO STUMBLES WHEN GIVEN THROTTLE. SLOWLY GETTING UP ON PLANE. THANKS FOR YOUR THOUGHTS.
- mrfixit643Lv 59 years agoFavorite Answer
It is normal for this to happen on older engines.It is unburnt fuel-oil and is not a problem.If you choose you can use a little less oil when mixing but I think it is better to have it smoke a little then to not have enough oil in the fuel.As for your stumbling when you accelerate you need to set your carbs or they need to be cleaned or rebuilt.
- jtexasLv 79 years ago
Not unusual. You have carbon build-up in the exhaust tube, probably in the cylinders, too.
Here's a good write-up on a "decarb" procedure. I use seafoam, but merc power tune, BRP engine tuner, yamaha ring-free, they're all good...
I also add an ounce of seafoam per gallon to the tank, it keeps carbon from forming. Using a prop that lets it make 5200-5300 RPM at full throttle helps, too.
Regarding your acceleration problem, it's probably time for a carb rebuild. Your carbs have two fixed jets each, no mixture screws to adjust. Carb kits about $12 apiece on iboats.com or ishopmarine.com, you'll be happy with the way she runs on fresh carbs.
It's customary to do a compression test and spark test first. Compression should be about the same on all 3, anything upwards of 100 PSI is good. Spark should jump a 7/16" gap on an inline tester clipped to the engine block.
That motor will run best with champion QL77JC4 at .030.
- Richard CLv 79 years ago
That's unburned fuel and burnt outboard oil that is exhausted into the leg of the outboard. That exhaust residue drips from the propeller area.
It's usually not a concern.