72 510 Electric Fuel Pump Issue

[CS310]

I replaced my Weber 32/36 carb on my 72 510 with a new one.  The mechanical fuel pump was also shot, so I decided to replace it with an electric fuel pump.

 

I’m having trouble with the electric fuel pump.  It doesn’t have enough “push” to get fuel to the carb.

 

Electric Fuel Pump Setup:

I used an Airtex 2.5-4psi rotary type in-line fuel pump.

Mounted just underneath the front of the fuel tank, behind the rear seat. 

I used the extra switched circuit in the fuse box for the hot side.

I ran the ground side through an inertia switch mounted under the dash.

I used a Russell 40 Micron fuel filter between the tank and pump.

I used a clear stock type paper fuel filter between the pump and carb.

I use ¼ rubber hose for inside fuel lines.  I used the stock hard fuel line under the car.

 

Result:

When I turn the ignition, the fuel pump starts as it should, but very little fuel makes it to the clear paper filter and it took several minutes to get there. It filled the filter to just below the element.  In addition, the pump got hot.

 

I tried each one of the ideas below, one at a time, with no improvement.

1. Removed the paper filter.

2. Bypassed the fuse box and ignition switch. Ran hot right to the battery.

3. Removed the Russel 40 micron filter.

4. Installed an AC Delco 2.5 - 4psi in-line electric fuel pump.  Same as installed on “Zeke”.

 

Other things I checked.

1. Disconnected the fuel line at the carb. Ran the pump. Very little fuel, took several minutes to get there.

2. Check the float chamber. Very little fuel.

3. Confirmed 12v at the pump.

 

Any thoughts would be appreciated. 

 

[bilzbobaggins]

Clogged inlet coming out of the tank.  Can you easily suck fuel up with a mity vac?  

 

Thats my guess if a known and verified good pump will pull only a little fuel up.  

[datzenmike]

Well run the pump with a good supply like from a separate container. This will do two things...

 

Prove the pump actually does work properly.

OR

Prove that the tank has a supply problem. Some sort of restriction.

 

If it does the same thing with a second pump it seems likely that it isn't the pump.

 

Fluid pumps can by built that produce thousands of pounds pressure but the strongest pump ever made cannot suck fluid up a pipe more than 30 feet vertical. This is because it is limited by atmospheric pressure... about 14.7 PSI. Pumps can easily push but they suck at sucking. ANY restriction on the inlet side reduces the pump's efficiency. Always mount as low and as close to the tank as you can.

[banzai510(hainz)]

buy a 20 Fuel pump stock clone for 20$

 

 

was is working before? so why would it be clogged?

 

 

try it with out he gas cap on.(im guessing now

 

 

you hooked the fuel pump to the return line by mistake

Edited October 11, 2019 by banzai510(hainz)

[CS310]

I appreciate the ideas. This is what I’m thinking. I’m going to disconnect the out line from the pump and see if anything changes. I will also try to remove the gas cap. By doing this it should eliminate the fuel line under the car. If no change, I will test the pump using a gas can.  If the pump works, it must be a problem with the tank.

 

The car ran before, but not very well. There could be some problem with the tank. 

 

Im using the lower outlet (smaller diameter) in the tank. I think the return line is the top one (larger diameter), correct?

[datzenmike]

Return line is always larger, yes.

[CS310]

It’s been several months but I finally found time to work on my 510 and run some tests.  I wanted to share my results.

 

1. I disconnected the fuel line after the pump.  Turned on the pump and the flow wasn’t that great. I removed the gas cap. No change.

 

2. I removed the pump and put the inlet hose in a full gas can, the outlet hose in an empty gas can and turned on the pump.  The flow was excellent.  Based on these tests, it appears I have some type of restriction in the tank.  I removed the tank and had it cleaned and sealed by a local shop.

 

I installed the cleaned and sealed tank using a new hose and the electric fuel pump I previously tested.  Assuming the tank was the only problem, I connected everything up to the engine compartment.  My plan was to turn on the pump and purge any junk that might be in the hard line before connecting to the carb.  I did this and the flow was almost zero.  It was a minute or so before any gas would come out.  I went back and disconnected the fuel hose after the pump and tested the pump again.  The flow was strong.  It appears the hard fuel line has some type of restriction or build up as well.  I visually inspected the hard line.  I didn’t see any damage so there must be some blockage.  At this point, I decided to replace the hard line.

 

I ordered a roll of 5/16 aluminum tube.  I removed the original hard fuel line and used it as a guide to bend the new aluminum line.  I started in the middle and worked my way out.  I used zip ties to hold the two lines together.  I used a 90 degree tube bender and spring to bend the aluminum line.  I used a beading tool to flare the ends for rubber hose and a deburring tool and scotch-brite pad to clean the ends.  I replaced the stock fuel line mounts with 5/16 stainless mounts.  I used the same mounting holes. The entire process went quick.  Less than a day from start to finish.

 

I connected everything again up to the engine compartment.  I wanted to run the pump and purge any aluminum debris left over from cutting the line.  I had strong flow as soon as I turned on the pump. I finished the connection to the carb. I cranked the engine and it started immediately.  Nice.  Time to tune the carb.

 

I appreciate all the advice.

 

The image below shows the current location of the electric fuel pump.  This is under the car in front of the right rear suspension arm.  Nice gravity feed from the tank.