I don't agree with the guru. If you look at the path that a fuel line goes through to get to a mechanical pump, sucking up out of a pickup tube, twisting and bending around crossmembers and obstructions, going through valves (if applicable, like my F250) and uphill to the pump, if it truly was a gravity setup, like a Model A or T, you wouldn't need a pump.

 

Electric pumps do need to be at or below the bottom of the tank, they are really poor at suction.

 

YA'LL TIRED OF THIS YET ??? I SURE AM !!!


SO THEN...

I plumbed up the edelbrock pump from a gas container with it's outlet at the bottom of the container so it would be ABOVE the pump to give it gravity flow.. As soon as the pump got the bowls filled the engine fired right off. So I know I have a good pump and plumbing to the carb.

We've pretty much eliminated the ignition since I've replaced every ignition component that I could... and it fired off (see above).

After discussing this problem with several people off the net and this esteemed group, my braintrust have about concluded that the up and down route my existing line takes is the problem. With the tank full or nearly full there is enough pressure (i.e. weight of fuel) in the tank for force the gas over the 8" rise and into the hardline. but when the pressure (weight) gets marginal, the mech pump can not pull it over the rise. Maybe it gets a good splash when braking or a trickle down the line as the truck moves down the road, which is enough to keep the bowls full at cruise or normal throttle. But when my foot gets into it... the trickle flow can't keep the 4 barrel fed and it stumbles and stalls from lack of fuel.

SO, it was suggested to add an electric pump back at the tank to get the fuel over the hump and keep an adequate flow of fuel to the mechanical pump. One suggested a click clack pump that goes inline back at the tank, but I couldn't find one with good reviews on longevity ... lots of comments about them lasting 1-2 weeks and some even 1-2 days...and that was across brands (which are mostly the same pump with different badging)

As an aside...during my research I asked Edelbrock, Holly, Jegs, Speedway and Summit and not one had a clue about the vacuum reading on the input side of the fuel pump, although all of them said that there WAS vacuum. Somebody should know that answer.

I ordered a Holley Sniper low pressure pump (not an EFI model) that had 96 GPH at 5-7 psi. I'll mount it in front of the tank with it's input at or below the tank fuel outlet level... and it can push the go juice to the front.

Of course that includes finding something to mount it to (it's crowded back there)...mounting it where the tank o/p is higher than the pump i/p... then doing the wiring and the plumbing...but the plumbing will probably be all rubber flex lines and screw clamps. later.... the pump came in Saturday but it will probably be Monday before I can get to it...prior commitments... I have no control or input into my scheduling... so Monday will be my first schedule opening (unless something else jumps up that has to be dealt with then)

I'll post progress pics as work progresses and will document the hell out of this for others. In my research I found nothing that addresses this problem with the Mustang tank riding low in a 53-56 frame. Surely someone has had this happen before... or maybe I'm just lucky.

This documentation reminds me of the story of the Sunday school teacher for the 3-4 y.o.s and she asked a little girl who was busy coloring what she was drawing. Little girl replied "It's a picture of Jesus" . The teacher told her that nobody knows what Jesus looked like to which the little girl announced "Well, they will in a minute !!!" So the internet presence will be along 'in a minute'.

more to come

 

⚠️ WARNING ⚠️ Please do not have an electric pump pump to/through a mechanical pump as some have/will suggest. When (not if) the mechanical pump diaphragm fails, the electric pump will still pump gas and will now quickly fill your crankcase leading to what will likely be a very big repair bill. On a mechanical only setup when the diaphragm fails, so does the pumping action and thus the engine becomes starved of fuel brining everything to a stop allowing for the issues to be addressed before major damage.

 

I think your problem might be the fuel filter and shut off you have in the suction line. It may be causing a restriction to the pump, Ford put the filter after the mechanical pump on carbureted engines.

 

When I saw how he had it plumbed I was thinking the same thing.
Other than a plastic screen we call a filter sock on the tube of the pick up inside the tank there is NO FILTERS on the suction side of motor driven fuel pumps and no shut off valves either. Easy enough to test I would think, remove both and add hose between the to hard lines and test.

Now I did have something that was strange when I went to get my truck running when I was rebuilding it.
Motor driven pump on a 300 six that worked a few months before.
I had a can up on the inner fender well and a hose from can to inlet of pump and it would not pull gas from the can.
Thinking the pump dried up over the few months, I replaced it and still could not pull fuel WTH???
Being the can was above the pump it should have pulled fuel with ease.

Thinking it may be pulling air at the pump I put a 2nd hose clamp on the hose, nope still would not pull fuel from can.
I was using 3/8 rubber hose as I had some long enough to do the job. I got some 5/16 hose from can to pump and used 1 clamp and it pulled fuel!!!
Even with 2 clamps it was still pulling air so make sure you are using the right size hose for the hard line on your truck.

I think before I used a hose between the 2 lines once the filter & valve have been removed I would put your gas can under the truck with a hose to the front hard line and see if it pulls fuel, it should if the rest of the line has no air leaks.

WAIT you are using SS braid at the fuel pump from the hard line?
I have had older braided line dry up just sitting on the shelf and crack but you cant see it because of the braid.
It may not look as nice but use rubber hose and cover it with the fake braid.
Then try the above test again once the filter & valve are gone.

I say my money is on bad braided line
Dave ----

 

Have you checked the pickup in the tank to make sure the feed tube isn't rusty and porous?

 

Have you checked the pickup in the tank to make sure the feed tube isn't rusty and porous? Fuel pickup and filter in the tank are brand new and shiny clean

I think your problem might be the fuel filter and shut off you have in the suction line. Filter was removed and cleaned with no dirt/trash found... shut off is wide open and shows no restriction
The complete line was blown down with compressed air from the tank to the fuel pump end with no noticeable restriction.

WAIT you are using SS braid at the fuel pump from the hard line? Line is new and very flexible...it's only about 12" long and you can see light through it when you hold it up.

Haven't had time to work on it this week... other fires to beat down... maybe back on it Friday...

 

Just because the filter is clean and the shut off is open doesn't mean that they are not causing a restriction, any restriction on the suction side of pump will make it more likely to vapor lock.