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I have a 1978 mercury outboard 150 HP motor that run fine except when on full throttle it seems to loose power for a second then picks up again then looses power for a second then picks up again, what could cause this

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  • Anonymous Mar 24, 2014

    The engine lacks power to get on plane and top speed

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For the DIY boater it could be a number of possibilities - fouled plugs, old fuel, improper air fuel mixture or dirt in the carburetor.

Pull the plugs and check the color of the ceramic. Light tan is good. Dark and oily is an indication of misfiring, fouling and too rich oil or improper air mixture. Make a note of which plug came from which cylinder. If they're all about the same color (dark) replace them all. Properly set the electrode gap and install the plugs.

You could try spraying the intake with carb cleaner like "Gum Out"
to clean out the carbs too.

Drain and clean out the sediment bowl of the carb(s) test again.

If cleaning sdoesn't take care of the problem then you need to Reference a Mercury marine manual for initial air screw mixture settings, ie: air screw location and how many turns out are recommended.

Air fuel mix is adjusted by a screw on each carb. No more than a 1/4 to 1/2 turn should be made at a time. Test again.

Also when you store the motor for the season, get some "Gas Stabilizer" for the fuel tank. Mix the recommended amount in a full tank of fuel, run the motor for several minutes. This step will put the stabilized fuel into the carbs for storage.

Hope this helps.




Posted on Oct 05, 2009

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