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.

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  • 9 years ago
    Favorite 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.

  • jtexas
    Lv 7
    9 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...

    http://forums.iboats.com/showthread.php?t=158076

    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.

  • 9 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.

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