Electric Fuel Pump 4-7psi.

[Captain Crunch]

Hi All,

I have picked up a Holly fuel pump that operates at 4-7psi.

Is this too much psi for the needle valve to handle?

Do the filters drop off some psi?

I was thinking if it is I can put in a valve to choke the psi down. Do you think this will be effective?

Ultimately I was hoping to put my electric fuel pump in as a back up on a 3 way valve in the fuel system. If my mech fuel pump drops out I can flip the valve, switch on the elec. fuel pump(series switch with the OPSS circuit) and keep going. Half baked idea?

Until I re-build my mech fuel pump I was going to run on the elec. fuel pump, im a little concerned with the psi.

Thanks in advance for the help!

CC.

[Dave Neptune]

The pressure a pump makes is the pressure it makes! Restricting the flow will actually increase the pressure a bit not lower it. It can be reduced with a "regulator". By the time you do all that the correct pressure range pump will cost less and be simpler as well as BETTER.

The carb could probably handle the pressure fine, but that just pushes it closer the the edge.

Dave Neptune

[joe_db]

Exactly plus it isn't very hard to find the correct pressure. My pump runs about 4.5 PSI and that is plenty. Actually 1 PSI seems fine too, our engines don't use much gas, it isn't like feeding a big block V8
What is wrong with your mechanical pump? Fixing that might be a better use of time and money.

[Captain Crunch]

Thanks for the reply's.

I was experiencing intermittent loss of power/rpm's, and eventually stalling. I had to get the boat back in with the dingy motor.

BTW, I highly recommend an outboard motor bracket on the transom for the dingy motor. This made getting the boat to safety a breeze...and very good piece of mind.

The engine ran great for the first two seasons I owned it. Then I started having problems that could have been from:

- dirty carb
- sticking needle valve
- failing fuel pump
- dying coil
- air leak in the fuel system
- or whatever else might cause my loss of power/rpm's and stalling while at cruising speed issues.

Any other suggestions?

I started going through everything and found lots of loose stuff, and started tearing things out, cleaning and replacing.

I decided to add a electronic fuel pump as a back up and to use while I wait for a rebuild kit for my mech fuel pump.

I will monitor the carb when I prime the system and see if it overfills.

CC.

[joe_db]

The throw everything at the wall and see what sticks system of engine diagnosis and repair can be troublesome, you'll never be sure what you fixed or what new problems you caused vs, old ones returning.

This has been a common theme for many years if not decades, the engine randomly stops and no one knows why. What you need is DATA. I have both a fuel pressure gauge and a fuel filter vacuum gauge and have solved issues that would take 100 years to find otherwise. Moyer even has a kit specifically for this issue:
https://moyermarine.com/product/the-...m-ktas_01_564/


You certainly can plumb in a system with an electrical and mechanical fuel pump. I would not do it aircraft style with the pumps in series, if the diaphragm starts leaking into the crankcase and you hit the electric pump switch it will be bad

[Sam]

I'll say it- 4 to 7psi is two much. Surprised you don't smell gas fumes as I had in the distant past with 3 to 7 psi. If you have a long run from tank/filter to the pump [like in a friends ODay] 4psi works well. I have an electric Facet 2-4psi and the fuel pressure gauge shows a fairly steady 2.5 -2.75 and the engine runs well. I 've always been told that the A4 carb only needs 1 or 2 psi. I have gone through three electric pumps in about 40 seasons. Never thought installed backups would be a concern, but I do have one stored on board.

[edwardc]

Originally Posted by Captain Crunch

... Ultimately I was hoping to put my electric fuel pump in as a back up on a 3 way valve in the fuel system. If my mech fuel pump drops out I can flip the valve, switch on the elec. fuel pump(series switch with the OPSS circuit) and keep going. Half baked idea?...

One of the typical ways an A4 mechanical fuel pump fails is for the diaphragm to leak. The pump is designed so that such a leak goes into the oil pan, NOT into the bilge. This is a safety factor so you don't fill your boat with gas fumes and risk going BOOM.

With gas in the oil, I don't think it would be a good idea to switch to an electric pump backup and keep on going.

[Captain Crunch]

Thanks again.

I am using a OPSS. I have not put the fuel system back together yet and I will take the advise of not running the electric fuel pump in series through the mech pump.

How about plumbing it in between the mech pump and the carb?

I have also been spending money on this site. A few hundred at this point. My issue right now is it took a month for my last order to arrive, a handful of gaskets and a overhaul manual. I believe the postal systems in both countries are experiencing Xmas like volume and delays.

I have found a good pressure regulator for the pump I have, and I have two mech pumps. I should be good. I will rebuild the one I got with the boat for piece of mind.

Thanks again!

CC

[joe_db]

We all are cheap, we're sailors That said, I am not sure my boat would be usable absent Moyer, so many of us feel compelled to give them a shout out when we can

The safe way to run two fuel pumps is this. You need to be able to cut the mechanical pump totally out of the system and you need a gauge or warning sensor to know when it needs doing.

[Surcouf]

technically, these would be the 3-ways valve, not 2-ways valve
But spot on for the proper configuration.

[joe_db]

Originally Posted by Surcouf

technically, these would be the 3-ways valve, not 2-ways valve
But spot on for the proper configuration.

Oops

This is how Piper does it. It works fine, but there is a failure mode for a boat engine that would pump all the fuel into the crankcase
* Do you see the fuel line running off the page from the primer? I once found one of the primer lines broken right at the manifold, so if I had used it I would have sprayed gas all over the engine