Re: 1981 Mercury 18hp.

[jerry-ahrens]

quote Shane.R13:

quote Jerry Ahrens:

Sounds like you are describing the Back Drag Jet in the throat of the carburetor. And yes that needs to be in there. The carb kit # is 1399-8153, I believe, and you will also need a 1399-8154 fuel pump rebuild kit. But I would need your serial # to be sure. One thing I can tell you is you probably need a good carb rebuild, along with a fuel pump diaphragm and the gaskets replaced. Pay close attention to the fuel pump parts and how they go back together… they are super easy to mix up. That and the fact that there are different style gaskets and check valves that must be replaced withe the correct parts. Also, check the fuel filter bowl gasket (O-ring) for vacume leaks. It may not leak fuel, but can have a vacume leak present. That would cause a bog problem.. Is your fuel line from the tank to the motor a bright silver color with red printing on the side?? If so, put it in the trash, cause if it hasn’t already failed, it will! Those hoses are notorious for falling apart inside, thus causing a fuel restriction. Just a few things you might think about.

Just curious Jerry as to why you would suggest a fuel pump kit? I seems to idle and run fine when I cover that back drag jet slightly. To my untrained self it seems like the fuel pump works fine. Just curious to your rationale before i start ordering parts. Thats all. I have had the fuel filter bowl off multiple times so thats likely is a wise idea to replace the or ring in it. No the fuel line isn’t silver and I’ve tired 3 tanks and 3 sets of lines thinking maybe it was a tank issue and no change in the motors behaviour.

To answer your question on the fuel pump…. those fuel pumps are tiny and don’t pull all that much fuel anyway, compared to a larger say, OMC one. If the diaphragm or gaskets are deteriorated, you could experience high speed bogging, or even problems at idle. On an engine that old, I replace all that stuff, along with a carb cleaning and a new impeller. That way your motor will be dependable. Fix it right and be done. If you do a carb rebuild, it will be easy to go ahead and do the fuel pump. BTW, I just checked your serial # on the Mercury Marine EPC….. parts look up. The part #s I gave you are correct for your motor.
Another question for you… How far away from the outboard is your fuel tank? If you are running this motor in a test tank or barrel, you need to get the fuel tank up off the floor, closer to the motor. Those little fuel pumps won’t lift fuel that high.