Fuel Pump rebuild Question/Problem 1985 75hp Merc

larrymm · Jul 31, 2009

I have a 1985 75hp Merc. In trying to rebuild the fuel pump I've run into a problem. It's the "triangular" fuel pump. When I removed the fuel pump boat was in the water and I may have lost the spring & button that pushes against the rubber diaphram (or it may not have been in there at all). I have the rebuild kit and also purchased a new spring & button but I cannot figure out how to anchor the spring or what it attaches to. I've looked at a few on-line parts sites to view the diagrams but they don't really show me what I need. I have the Seloc manulal (last time I do that) and that doesn't even show the spring & button assy. Can anyone give me any ideas & advice or pics/diagrams of the inside of the pump?
Thanks

Chris1956 · Aug 1, 2009

Re: Fuel Pump rebuild Question/Problem 1985 75hp Merc

Larrry, I have never worked on that kind of fuerl pump, however, Merc will normally put a definite seat in the casting fro the spring. Look at the top cover, after the check valves are installed, and try to locate a spot that would naturally hold the end of the spring.

Best I can do....

al9981 · Aug 1, 2009

Re: Fuel Pump rebuild Question/Problem 1985 75hp Merc

Hope this will help
http://www.usboatsupply.com/Mercury_Mercruiser_Parts_Catalog3a.php?mc=02&ms=5020&si=277

larrymm · Aug 1, 2009

Re: Fuel Pump rebuild Question/Problem 1985 75hp Merc

Merc is usually pretty good but there is no seat or indentation that I can find nor is there a nub or stub that the spring can sit on, it's strange.
Al, thanks for the link. This is a good parts explosion but it doesn't go into enough detail to see where the spring actually goes. The plastic button rests against the diaphram but the other end is still a mystery.
Thanks for the responses.

al9981 · Aug 4, 2009

Re: Fuel Pump rebuild Question/Problem 1985 75hp Merc

I ordered a rebuild kit for my fuel pump and I will keep you in mind when I get to the spring and how it is attached. I will make sure I do it at home and not on the water.

red cobia 17' · Aug 4, 2009

Re: Fuel Pump rebuild Question/Problem 1985 75hp Merc

Have you tried to talk to your local dealer and see if they will show where it goes?

al9981 · Aug 5, 2009

Re: Fuel Pump rebuild Question/Problem 1985 75hp Merc

Larry, I rebuild my fuel pump this after noon and it was piece of cake. It took about 15 min. I took some pics and I wasnt sure how and why you got the springs out of thing.
View attachment 34858
Whole assembly before I took it apart.

al9981 · Aug 5, 2009

Re: Fuel Pump rebuild Question/Problem 1985 75hp Merc

I took the first plug out. and there it is. Replace the gasket on it. And go to the next one. As in the first pic, they need to be in the opposite direction of each other.

al9981 · Aug 5, 2009

Re: Fuel Pump rebuild Question/Problem 1985 75hp Merc

If you are talking about the spring inside these plugs. They are locked inside the plug. It looked like there is the plastic white part, then the spring then the top metal which locks on the bottom piece.

larrymm · Aug 6, 2009

Re: Fuel Pump rebuild Question/Problem 1985 75hp Merc

Al thanks for the update & pics, glad it went well for you.
It's not the spring inside the check valves that I'm having problems with, it's the spring that is attached to the plastic button or cap that pushes against the diaphragm. If you take a look at the link you sent me (US Boat Supply), check the diagram for 75hp Merc. 4 cyl, ser #643xx w/triangular fuel pump. The spring is #6 and the plastic cap is #7. It's that spring that I cannot figure out what it sits on or attaches to. Do you remember seeing it in your fuel pump? I did not have it in mine and I figured I lost it overboard while I was pulling the pump off. Except for this part, I agree that the rebuild is a piece of cake!
Thanks again!

al9981 · Aug 6, 2009

Re: Fuel Pump rebuild Question/Problem 1985 75hp Merc

Dude, I did not have that in the fuel pump. I took it apart nice and easy and I did not have anything over the little plate with the two screws. I even have them on my diagram, but they are not in the pump. Same as the fuel filter, I don't have it on my lines. So I am not sure why we dont have it or what it is for

larrymm · Aug 6, 2009

Re: Fuel Pump rebuild Question/Problem 1985 75hp Merc

So maybe I didn't loose it when I removed the pump, possible it's only on certain engines (maybe larger engines that use this fuel pump)??
As for the fuel filter, I don't have one either. Only a metal screen inside the cover of the fuel pump.

al9981 · Aug 7, 2009

Re: Fuel Pump rebuild Question/Problem 1985 75hp Merc

Larry, I took my boat out for a spin yesterday and it ran fine. I still need to test it with pulling a tube to see if it s going to take all that load. As for the fuel filter, I think i am going to add a filter before the fuel pump just because I am using a metal gas tank. And every time i open up the carbs, I find dirt from the gas. I hope I ll have some time on the weekend to give it a good test.

larrymm · Aug 7, 2009

Re: Fuel Pump rebuild Question/Problem 1985 75hp Merc

Good to hear, hope you're up & running!

temple1975 · Oct 25, 2015

This is a very old thread but still helped me this week. The spring cap is used in later serial number engines. I assumed they improved it from the original design. If you use the cap / spring you also need to update the actual fuel pump housing. If you don't have the housing apparently it is not needed. The question I have is why the change ? We have to assume the update housing and spring / cap combination improves some aspect of fuel delivery. ( SEE ATTACHED )

Fuel Pump rebuild Question/Problem 1985 75hp Merc

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