Fuel pump siphon? - Ford Muscle Forums : Ford Muscle Cars Tech Forum
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post #1 of 13 (permalink) Old 10-27-2017, 10:55 AM Thread Starter
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Fuel pump siphon?

I recently installed an airtex 9 psi fuel pump in front of my mechanical. When the carb is dry, 10-15 seconds will enable a quick start. I have noticed though that the car will idle for a few minutes, then die. When I check the bowl it is near empty.

However, If I keep the idle high for a couple of minutes (not really what I want to do), then it stays full. Here is a diagram of my setup. Any thoughts on what is wrong?
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Putts drives a 1965 customized Galaxie. Rebuilt 390, 4100 electric choke on a Performer, MX, AC, PS, PB w Scarebird front discs on Cragar 17" S/S.

Last edited by puttster; 10-27-2017 at 02:29 PM.
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post #2 of 13 (permalink) Old 10-27-2017, 12:06 PM
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Re: Fuel pump siphon?

I suspect that the electric pump motor needs more voltage then it's getting at idle. It has plenty at "key on" since nothing else is running. At idle many alternators don't make enough juice so the pump may be seeing a significant voltage drop. At higher engine speeds the alternator makes plenty of power. To test, use a voltmeter at the pump. To correct, consider using a large wire right off the battery through a relay to power the pump.

An unrelated concern: 9psi at the carburetor may be too much. Check with the manufacturer. OEM cabs typically only like to see 5. You might consider a pressure regulator.

1964 Thunderbird 390 V8, AOD, F.A.S.T. EZ EFI 1.0, Victor intake, MSD Ignition.
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post #3 of 13 (permalink) Old 10-27-2017, 12:23 PM Thread Starter
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Re: Fuel pump siphon?

After priming, I turn the electric pump off and let the mechanical take over.

Putts drives a 1965 customized Galaxie. Rebuilt 390, 4100 electric choke on a Performer, MX, AC, PS, PB w Scarebird front discs on Cragar 17" S/S.
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post #4 of 13 (permalink) Old 10-27-2017, 01:25 PM
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Re: Fuel pump siphon?

OK. In that case I suspect that the mechanical pump is causing enough restriction to prevent the mechanical from doing its job at idle speed.

1964 Thunderbird 390 V8, AOD, F.A.S.T. EZ EFI 1.0, Victor intake, MSD Ignition.
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post #5 of 13 (permalink) Old 10-27-2017, 04:31 PM
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Re: Fuel pump siphon?

tom.. why dont you set it up like JC did on his....
with a bypass and check valve...
that way your mechanical pump dont have to draw/suck the fuel thru the electric pump after engine is started...


%201964%20Galaxie/?action=view&current=09-03-10_1408.jpg Lars...
64 galaxie 500 2dr fastback...390 4v, Bendtsen adapter, maddog's stage3 700R4 trans,3.70 Posi..far from perfect but getting there...
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post #6 of 13 (permalink) Old 10-27-2017, 05:46 PM Thread Starter
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Re: Fuel pump siphon?

Once the car gets over the first few minutes, it's fine, I can drive around at 2500 rpm, no problem. That's why I don't think the electric pump is restricting flow.

Seems like after I run the pump there is a empty spot somewhere and if that spot doesn't fill up before the float bowl empties, the car dies.

Putts drives a 1965 customized Galaxie. Rebuilt 390, 4100 electric choke on a Performer, MX, AC, PS, PB w Scarebird front discs on Cragar 17" S/S.
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post #7 of 13 (permalink) Old 10-28-2017, 02:59 AM
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Re: Fuel pump siphon?

Leave the electric pump running until the engine is warmed up....then turn it off!!

I suspect you get some aeration with the electric pump until it picks up a solid stream of fuel!!
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post #8 of 13 (permalink) Old 10-28-2017, 09:50 AM Thread Starter
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Re: Fuel pump siphon?

Yeah, I was wondering where the air was hiding. Maybe in the long line from the electric to the tank?
Well, I took her to the Exxon and put 17.1 gallons in there, so maybe having only 2.9 gallons in the tank was causing the issue.

Putts drives a 1965 customized Galaxie. Rebuilt 390, 4100 electric choke on a Performer, MX, AC, PS, PB w Scarebird front discs on Cragar 17" S/S.
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post #9 of 13 (permalink) Old 10-31-2017, 05:16 AM
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Re: Fuel pump siphon?

I would have put the fuel pump before the mechanical pump as close to the tank as possible. Guys usually put one on their cars that sit for a week or so. They usually wire them to the starter crank circuit so it only runs when the engine is being cranked over to start. I agree that 9 psi is a bit much at the carb. My .02
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post #10 of 13 (permalink) Old 10-31-2017, 03:40 PM
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Re: Fuel pump siphon?

Hi there,

It might be restricting enough if the stock pump is a little weak.
I put mine at the tank. There is no switch so it's always on.
No problems.

Mel

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post #11 of 13 (permalink) Old 11-01-2017, 02:35 AM Thread Starter
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Re: Fuel pump siphon?

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Originally Posted by Nite-owl View Post
Hi there,

I put mine at the tank.
Mel, where exactly? Thx.

Putts drives a 1965 customized Galaxie. Rebuilt 390, 4100 electric choke on a Performer, MX, AC, PS, PB w Scarebird front discs on Cragar 17" S/S.
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post #12 of 13 (permalink) Old 11-01-2017, 07:21 AM
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Re: Fuel pump siphon?

Quote:
Originally Posted by puttster View Post
Mel, where exactly? Thx.
You don't just let it dangle off a hose.

Fuel Pumps and Accessories

These brackets set the pump at the proper height and the suction in a little "bath tub" that helps keep it immersed in fuel when the level is low and under acceleration forces.

They make tanks with brackets for many popular models. If yours isn't on this list (mine wasn't), you'll spend considerable time adapting a tank, so it's usually best to buy a new tank instead of modifying an older tank.

1964 Thunderbird 390 V8, AOD, F.A.S.T. EZ EFI 1.0, Victor intake, MSD Ignition.
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post #13 of 13 (permalink) Old 11-02-2017, 09:26 AM
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Re: Fuel pump siphon?

Hi there,

My pump is mounted on the tank, on the lip that are the two halves of the tank, real close to the fuel hose. There was allready a hole there. Cut the hose and put the pump in between. Power from the ign. switch.

Mel
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