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  #1   IP: 75.176.18.51
Old 03-06-2023, 09:26 PM
Marty_B Marty_B is offline
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Electric Fuel Pump

Hi All,
I recently acquired an Irwin 28 with an Atomic 4 engine. The wiring for this engine has many cut wires and is a mess. I have since taken the engine out and have it on a stand. I noticed that it has an electric fuel pump, but it is not connected electrically. I also noticed that there is no oil pressure safety switch.
With that being said, I have two questions,
1) first, is it better to have the oil safety switch installed above the pressure adjustment screw or where the oil sending unit is?
2) I have heard that an electric fuel pump sometimes requires a return to tank line. My boat currently has no such line. I have read that the carb needs about 1 psi of pressure to run correctly. At what pressure would a return/bypass line be required?

Thanks for your help.
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  #2   IP: 162.245.50.243
Old 03-07-2023, 08:44 AM
Dave Neptune Dave Neptune is online now
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The first thing you need to know is "what pump" you have? The specs will let you know pressure and volume.

1 psi is not enough for good performance but it will run at low engine speed and load. 2~3 psi is very good.

I have not seen a return line on an A-4 but heard of a couple who installed one, One was for vapor lock however I don't see how a marine engine could need one unless it was really overheating and some use it a polishing mechanism.

As far as the OPSS mount it where it is the most convenient for your installation regarding future maintenance.

If you are in doubt about your pump best to get one of the proper rating from our host as it will "be correct".

If the current pump was not wired how did it work or was it just mounted as a spare incase the stock pump failed?

Dave Neptune
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  #3   IP: 75.176.18.51
Old 03-07-2023, 11:50 AM
Marty_B Marty_B is offline
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Thanks for your quick reply and input. I think the current pump is rated at 1-4.5 psi. It was not wired and the engine did not run when I got it. There were a few components missing from the engine as well, such as the alternator. Also the fuel supply was not connected to it. I am not even sure that it works.
I took the engine out so I can have better access to the engine compartment and fuel tank as I plan on removing it for restoration/replacement.
Thanks again for your help.
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  #4   IP: 138.207.177.95
Old 03-07-2023, 02:41 PM
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The engine will tolerate a wide range of fuel pressure. When you go to high, you risk leaking past the float valve. I accidentally got 9 PSI once experimenting with a pump and it seemed OK for the 15 minutes or so I had it on.
You can go as low as 0, the engine will run for a bit on the fuel in the carb. What happens with low fuel pressure is the engine stumbles with rapid throttle advancement. Ideally you want about 3-4 PSI showing.
The A4 does not normally have a return line. There are three reasons to have them:
1. To purge air when installing a new filter.
2. To use for fuel polishing.
3. To eliminate vapor lock.
1 and 2 are useful, 3 is probably not needed for most people. I do need it, I still am not sure exactly why my installation is prone to this issue. No A4 I have ever seen uses a return off of a pressure regulator like many cars do. I do not think a marine version of such a regulator exists.
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