posted 01-31-2010 11:06 PM ET (US)            

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I have to theories both tied to the carbs (and fuel). A small adjustment is hopefully all you need.

First Theory - The idle fuel mixture is a little on the lean side. When you go to "punch it" there isn't enough fuel with the increase air volume, and the motor starves and cuts out. To fix this, adjust each idle screw on the carbs. My guess is you don't need much, may a 1/8 of a turn CC. (Make sure to note exactly the position the screw started. You may want to return to that point) -- And you can adjust the screws while in idle. You don't want to run to rich, and dump too much fuel in; you can hear the engine bog down when this happens. (Nor do you want to run lean, and not provide enough oil.)

Second - The carbs are simple dirty (and maybe the fuel is old too). Run some fuel cleaner. Quickleen is the Merc brand, but anything similar will work. (Just make sure it is meant for 2-S.)

posted 02-01-2010 10:15 PM ET (US)            

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Yes, I was wondering (after I offered advice to check the spark gap) if this motor was set up with the very wide surface gap (also known as gap-less) spark plugs seen on many Mercury outboards.

The reason I mention spark gap--in several years of running my two-cycle carburetor motor, I noticed that whenever the motor seemed to have a tendency to stumble on acceleration, the spark plug gap was always out of tolerance, that is, wider than the recommended setting. Returning the spark plug gap to the recommended (and narrower) setting produced an improvement in the motor under hard acceleration.

Of course, insufficient fuel supply is also a very likely cause of trouble in getting the motor to accelerate. I am not familiar with the carburetor set up on Mercury motors. I don't know if they have any sort of fuel enrichment circuit that tries to assist acceleration. Dirty carburetors and poor fuel quality are very likely causes. However, I think it is reasonable to verify the spark plug condition, too.

posted 02-02-2010 01:44 AM ET (US)         

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Bogging down on acceleration is almost always the result of carb low speed jets set too lean. Alcohol in fuel can affect this also.

On each carb, turn jet clockwise until they seat lightly in a full lean situation. Then back off 1-1/2 turns counter clockwise. This should provide a smooth idle and smooth acceleration. You can then further fine tune the adjustment, if necessary, with the engine ilding in gear at 600 RPM. If this doesn't work, have your carbs fully serviced by a dealership. You could have clogged jets and fuel passages leaning out the mixture.