Electric fuel boost pump

[High Flyer]

Hi Guys - Re: 3.0ltr Mercruiser; has anyone found fitting a supplementary in line electric fuel boost pump a benefit, I'm thinking prior to start and getting the fuel up to the carb., we find that the recommended two/three pumps of the throttle lever is just not enough - will the electric pump on initial start help - John

[mmwjr]

Do you currently have a mechanical fuel pump? In my experience the fuel evaporates out of the carburetor bowl and requires a few cranks to refill in order to start. Replacing the mechanical pump with an electric requires a oil pressure switch to be coast guard approved. In this case the pump gets power from the starter solenoid when trying to start and the oil pressure switch once the engine is running. This will still have the same problem. You don’t want to have both pumps in the system as the fuel pressure can be too high. The coat guard requirement is for fire safety as it removes power from the pump if the engine stalls. One solution would be to use the electric fuel pump as I described you can add a monetary switch at the help to run the pump filling the carburetor bowl, however you still need to pump the throttle a couple of times to prime the engine.

Frankly two/three pumps is normal and I would not change a thing.

[shrew]

Originally Posted by High Flyer

we find that the recommended two/three pumps of the throttle lever is just not enough

Does 4 full pumps improve the situation? On a carb'd merc, I would think 2 pumps, or pump strokes that are too short will not work.

[High Flyer]

Hi Mike - Thank you for your thoughts: were in the UK, with a Maxum 18, yes, standard mechanical pump is fitted (BTW, we don't have Coast Guard/Maratime Agency involvement with such things over here), my idea was to put a electric boost pump in-line (standard practice on low wing GA aircraft), to get the fuel all 'filled' up to the carb, prior to cranking, our engine takes a lot of throttle pumping to start, which cannot be right - John

[mmwjr]

John,

Coast Guard or not the oil pressure switch is a valuable safety feature to prevent explosions. Multiple starting attempts is fairly normal but does strain the starter. If you really want to use an electric pump I would get a ignition protected one (marine) rate for 7 psi and delete the mechanical pump. Then wire it as Mercruiser does but add the monetary helm switch to fill the carburetor before trying to start. Note you still need to pump the throttle a couple of times to prime the engine and set the choke.