Merc 4.1 Fuel pump problem

[ferg]

I recently purchased a remanufactured 1975 I-6 Mercruiser 4.1 250cid Longblock, which I've finally finished putting all together and put it back in my boat last week. When I tried to start it up, it just kept cranking and never roared to life, which I quickly discovered was because the fuel pump wasn't pumping any fuel.

It's a mechanical fuel pump, and when I take it off I can depress the plunger manually and gas will start shooting out of it. Also, looking at the camshaft through the fuel pump opening, there is definitely a lobe there that pushes the plunger on the fuel pump, but apparently it doesn't push it far enough? I can hold the fuel pump up to this lobe and have someone crank the engine, and the fuel pump will rock back and forth in my hand, so I know it's depressing the plunger at least a little bit. Also, the fuel pump worked great on my old motor - I never had any indication of any fuel problem.

My question is, is there a difference between a marine fuel pump and an auto fuel pump? Because I know there is a difference in camshafts. If the fuel pump types are different, is it possible than I paid for and received a marine block with an automotive camshaft?

Other question, if I have to buy a new fuel pump, is there any reason why I could not install an electric pump?

Thanks

 

[Bt Doctur]

Re: Merc 4.1 Fuel pump problem

Maybe the can has a worn lobe for the fuel pump. compare the lift with the old motors cam.

 

[ParallaxBill]

Re: Merc 4.1 Fuel pump problem

The fuel pump lobe of the camshaft will be the same for auto or boat. Those fuel pumps are different but the stroke to operate them is the same. Sounds like you have a fuel blockage somewhere downstream of the pump to me.

Are you getting good fire through the ignition?

Can you see gas shooting into the throat of the carb when you operate the throttle manually?

 

[ferg]

Re: Merc 4.1 Fuel pump problem

The fuel pump lobe of the camshaft will be the same for auto or boat. Those fuel pumps are different but the stroke to operate them is the same. Sounds like you have a fuel blockage somewhere downstream of the pump to me.

Are you getting good fire through the ignition?

Can you see gas shooting into the throat of the carb when you operate the throttle manually?

First, thanks for responding.

To check the fuel pump manually, I disconnected the fuel line at the carburetor and pumped the plunger by hand and gas came shooting out, which I figured eliminated a fuel blockage issue up until the carburetor. The carburetor is freshly rebuilt, so there shouldn't be any blockage in there either.

How am I supposed to see gas shooting into the carburetor? My line is all metal, with no clear ports or anything.

Regarding the plugs firing...I checked that by hooking up a timing light to the first plug, and it would fire every couple of seconds while the starter was cranking the engine.

Bt Doctur recommended measuring the cam lobe at its highest to see if my "new" one might be worn down. That seems unlikely due to it being remanufactured, as I doubt the reman company would miss that. However, I do plan to check the lift on the old one and compare anyway....but I need to figure out how to turn that old crankshaft....

 

[Coors]

Re: Merc 4.1 Fuel pump problem

How am I supposed to see gas shooting into the carburetor? My line is all metal, with no clear ports or anything.

Inside the carb throat.
I just looked at my '70's books, but all it said was that there were 2 fuel pumps made; servicable, and non.
But a leak between the pump and tank could cause the same problem; moving the lever by hand, you are increasing the stroke on the lever.
Don has a sticky in here for checking that.

 

[ferg]

Re: Merc 4.1 Fuel pump problem

I cannot seem to locate Don's sticky

 

[Bondo]

Re: Merc 4.1 Fuel pump problem

Have a Look Here,...............