Fuel System: Fuel Drain Back - fuel pump losing prime?

[Flat Ernie]

Now that I've drug my '53 Coupe out, I'm remembering little things that bugged me before.

If the car sits for more than a couple of days, it's like the gas has all evaporated and drained back into the tank. I have to crank and crank and crank, and lately, it's easier to just stuff an air hose down the fuel filler to force prime it. If it ran yesterday, it cranks right up, but after two or three days, it's painful.

I've got an Edelbrock 1403 on a 289 with a stock Carter fuel pump. Not sure if it's a bad check valve in the pump, a weak pump, or something else. The car has been sitting for about 7 years, but it has always done this since I've owned it.

If this is common, I'll put an electric pump back near the tank as a priming pump or something. Otherwise, if folks think a rebuild of the stock pump is in order, I'll do that (where do you get the parts?).

Thoughts? Ideas? Recommendations?

[larkregal62]

Very common you gave your own solution--it's the correct one There arer many threads here to suggest the proper pumps and the safest way to install them. Gordon

[altair]

I don't think the fuel will bleed back in to the tank, if you disconnect the inlet fuel line at the pump gravity will deliver fuel to that point. Your problem is most likely a pin hole in the fuel delivery line and the fuel is leaking out and the pump is sucking air. If the hole(s) is/are small enough the pump will overcome and the engine will run just fine. When it sits the air will displace the fuel and you will have problems starting. Pressurize the fuel delivery line with just ounces eg. blow on a rubber hose and spray the fuel line and clasps with soapy water and you will probably see bubbles. I had the exact condition, after two fuel pumps and two carburetors, I finally determined the fuel line was leaking, and it was. I had several holes and rusted areas. Even then the engine still ran but I had to prime it every time I started it. A new fuel line and problem solved.

[Flat Ernie]

I don't think the fuel will bleed back in to the tank, if you disconnect the inlet fuel line at the pump gravity will deliver fuel to that point. Your problem is most likely a pin hole in the fuel delivery line and the fuel is leaking out and the pump is sucking air. If the hole(s) is/are small enough the pump will overcome and the engine will run just fine. When it sits the air will displace the fuel and you will have problems starting. Pressurize the fuel delivery line with just ounces eg. blow on a rubber hose and spray the fuel line and clasps with soapy water and you will probably see bubbles. I had the exact condition, after two fuel pumps and two carburetors, I finally determined the fuel line was leaking, and it was. I had several holes and rusted areas. Even then the engine still ran but I had to prime it every time I started it. A new fuel line and problem solved.

While I won't rule that out, it's low on my list right now. The lines were all new and the car was stored inside for all but a couple months. About half the time was in New Mexico, so a very dry climate.

While trouble shooting last month, I blew into the line at the pump back toward the tank to ensure there was no blockage our leaks...and I recognize that the type of leaks you're talking about may not be obvious.

What is confusing is the carb itself going dry. Even if there were pin holes, the line between the pump and carb should remain full of fuel.

All that said, pin holes would definitely explain my symptoms. I've been working on old cars for thirty or forty years and have never run across pin holes in fuel lines. Rusted lines, cracked lines, plugged lines, bad flares, kinked lines, crushed lines, but never pin holes that didn't obviously leak or smell...I have neither...but they could still be there I suppose.

[StudeRich]

A good Original Carter Pump will hold the fuel about one week or more, if not I suspect the one-way Valve in the output Port.

The 10% Ethanol Fuel evaporation issue is way over stated here, yes it does over time, but not in a day or 2.

[Flat Ernie]

A good Original Carter Pump will hold the fuel about one week or more, if not I suspect the one-way Valve in the output Port.

The 10% Ethanol Fuel evaporation issue is way over stated here, yes it does over time, but not in a day or 2.

I agree on the evaporation...most of my old cars have open bowl vents and none have this problem. However, on the Stude, there is no gas in the carb. None. I don't see where it could leak out (other Edelbrock carbs don't exhibit this problem), and I don't see how it could siphon out either. But it's gone in a few days. So, I'm not certain what's happening.

Also, the inability of the pump to immediately fill the bowl and being difficult to pull fuel is troubling. It does fit the symptoms of a small supply line leak.

It's more annoying than anything. I've got bigger issues to fix...like pulling brakes.

[Mike Van Veghten]

And the more alcohol that the government puts into the gasoline, the faster it will evaporate.

An electric pump eliminates all the "cranking" before the system refills to start the engine.
Also helps eliminate possible problems with cam lubricant being wiped off the cam and lifters while the engine is spinning dry, trying to start, the oil being wiped from the cylinders by the rings while the engine is trying to start.

Mike

[Flat Ernie]

If I elect to put an electric priming pump in, am I right to assume the solenoid types are able to be drawn through? I know the vane and bellows types can't, and I don't think georotor can either, so that leaves the solenoid type...I probably have one somewhere...guess I can try it and see.

[RDWEAVER]

I have the same trouble here. Exactly. I use a 2bbl. Stromberg but have the same issues. I figured the heat from the engine was cooking the fuel from carb percolating it empty after I went into the house and sat in my chair. I just don't like the extra wear and tear on the starter so I may need to use an electric pump for peace of mind.

[345 DeSoto]

Think about it...HOW is the fuel going to get past the needle and seat in the carburetor and siphon back down to the pump. It's NOT. The vapor pressure of modern fuel is such that it evaporates out of the fuel bowl of the carburetor. The best way to remedy this is to properly install a low (3-4lb) pressure pump as close to the tank as possible. I've put a toggle switch under the dash, and use it to prime the carburetor before starting. You can hear it change tone when the carb bowl is full...then turn it off and let the Stock pump take over when the engine starts I've done this on ALL my carbureted cars, and it's CURED the problem completely. Turning the engine off when "hot", just after normal use, speeds the evaporation...

[Flat Ernie]

Think about it...HOW is the fuel going to get past the needle and seat in the carburetor and siphon back down to the pump. It's NOT. The vapor pressure of modern fuel is such that it evaporates out of the fuel bowl of the carburetor. The best way to remedy this is to properly install a low (3-4lb) pressure pump as close to the tank as possible. I've put a toggle switch under the dash, and use it to prime the carburetor before starting. You can hear it change tone when the carb bowl is full...then turn it off and let the Stock pump take over when the engine starts I've done this on ALL my carbureted cars, and it's CURED the problem completely. Turning the engine off when "hot", just after normal use, speeds the evaporation...

I agree. However this is the only car I've got with this issue. Ever.

I agree that the fuel is evaporating, however, none of my other carbureted cars have this issue. Even sitting for weeks.

But assume it's all evaporating within a couple of days. Why won't the fuel pump fill the bowl within a few seconds?

Seems like there's two problems.

I've got old Fords with Strombergs, wcfb, and even a Holley. None did this. I've run mostly Holley carbs on everything I've owned from muscle cars to old relics to EFI reversion...never had this issue. I've run Edelbrock carbs on a cars in the past and never had this issue. At most, if a car Sat for a month, I'd have crank for a few seconds to get some in the bowl, but that's it.

I realize an inline electric priming pump will cure the symptoms, but I'd like to know why...

[wittsend]

I've got the same problem as Flat Ernie. Even a few days and the bowl is empty on my Edelbrock carb. And as with his situation cranking endlessly doesn't seem to fill the bowl. Yet splash a little gas in the carb, turn it over and generally it will start right up. Once running everything is fine. BTW, the engine is a 350 Chevy and the Edelbrock a 1406.

One thing I did notice is that the bowl vent is rather large. On most early 70's and up cars there is closed (charcoal canister) system that it connects to. On older car most people just let it vent to the atmosphere. I wonder if that isn't a contributor to the gas evaporating.

On using the electric fuel pump as a "primer." Once the electric pump is shut off wouldn't it become a restriction to fuel passing through it? And likewise, on the front end, wouldn't the mechanical pump become a restriction unless the car was cranking (which we are trying to prevent) during the priming process? If neither is occurring then great, but could someone explain how? I've only opened an electric pump once (a Conelec) and the vanes would seem to inhibit fuel passing if it wasn't turning. I have one of those for lack of a better term "vibrating pumps" sitting around and maybe when they stop the plunger retracts allowing fuel flow???

[Flat Ernie]

I've got the same problem as Flat Ernie. Even a few days and the bowl is empty on my Edelbrock carb. And as with his situation cranking endlessly doesn't seem to fill the bowl. Yet splash a little gas in the carb, turn it over and generally it will start right up. Once running everything is fine. BTW, the engine is a 350 Chevy and the Edelbrock a 1406.

One thing I did notice is that the bowl vent is rather large. On most early 70's and up cars there is closed (charcoal canister) system that it connects to. On older car most people just let it vent to the atmosphere. I wonder if that isn't a contributor to the gas evaporating.

On using the electric fuel pump as a "primer." Once the electric pump is shut off wouldn't it become a restriction to fuel passing through it? And likewise, on the front end, wouldn't the mechanical pump become a restriction unless the car was cranking (which we are trying to prevent) during the priming process? If neither is occurring then great, but could someone explain how? I've only opened an electric pump once (a Conelec) and the vanes would seem to inhibit fuel passing if it wasn't turning. I have one of those for lack of a better term "vibrating pumps" sitting around and maybe when they stop the plunger retracts allowing fuel flow???

That was my question up above in post #8. I know rotary vane types will restrict. I know the bellows/diaphragm types will often restrict. I'm pretty sure the georotor pumps will restrict. But I believe the solenoid-based pumps will allow bypass.

As far as the mechanical pump, it should have two one-way check valves that should allow flow. I know that when I put an air hose in the gas filler neck, I can push the fuel up into the carb, so an electric pump should be able to do the same.

[jrlemke]

I have the same problem on my Hawk. I had it with the original WCFB and I have it with the AFB. I've used the AFB on three cars including the original, a '65 Buick 300ci, and a '56 Buick 322ci, and now my '61 289ci Stude. The only one that this happens to is the Stude. I'm using a "Mr. Gasket" low-pressure #12S electric pump from Auto Zone, about $45.-Jim

[christophe]

I've got the same problem as Flat Ernie. Even a few days and the bowl is empty on my Edelbrock carb. And as with his situation cranking endlessly doesn't seem to fill the bowl. Yet splash a little gas in the carb, turn it over and generally it will start right up. Once running everything is fine. BTW, the engine is a 350 Chevy and the Edelbrock a 1406.

I had this problem on my 63S (Carter fuel pump and 32 RBS carb). I finally solved it by eliminating the spongy filter located in the fuel pump bowl. Now, even after several weeks, the car generally starts at the third try.