Advice for electric fuel pump setup for flathead Cadillac

[Stude Light]

I’ve had an electric fuel pump on my 1939 LaSalle to help for starts and vapor lock. It was installed with rubber fuel line along the frame forward of the left rear tire. I’ve been wanting to hard pipe it and finally decided to do that.

 

I have tried about everything on this car to keep it from vapor locking including replacing the pump with a later model (supposed to be less prone to vapor lock), insulating the line from the pump and installing a heat shield between the carb and rear crossover.

It will occasionally vapor lock when driving once it’s really hot under the hood - usually when demanding some fuel (accelerating).

 

My next thought was to install a bypass around the pump with a check valve. This style pump should flow through but another route may help reduce the pressure drop on the inlet side of the mechanical pump which may help.

 

Here is my proposed setup (fuel line will have double flare joints).

I need to get all the nipples and a union still. My question is:

Should I be using a different check valve? I was planning on this Carter unit which has a light spring and seat design. It requires a small amount of pressure to open it. Maybe just a floating ball check? Does anyone have a recommendation or experience with this one? 
 

Also, feel free to chime in on anything else that doesn’t look right. The drain was to allow a way to pump the tank out if ever needed. Thanks.

Scott

[joe_padavano]

That's a whole lot of fittings and potential leak points. I would have selected inverted flare tee fittings and made my own hard lines, which eliminates the inverted flare-to-NPT adapters you have and also the need for a union as the inverted flare nuts perform that function.

[Stude Light]

1 hour ago, joe_padavano said:

That's a whole lot of fittings and potential leak points. I would have selected inverted flare tee fittings and made my own hard lines, which eliminates the inverted flare-to-NPT adapters you have and also the need for a union as the inverted flare nuts perform that function.

Thank you for the input, Joe. It is a lot of joints. I considered flare joints but I would have needed adapters for the pump itself so it just eliminates the union and maybe the elbows. With pipe threads I get a more compact setup.
 

I decided to add a pressure regulator too so I can run the electric pump all the time if needed.

[joe_padavano]

1 hour ago, Stude Light said:

Thank you for the input, Joe. It is a lot of joints. I considered flare joints but I would have needed adapters for the pump itself so it just eliminates the union and maybe the elbows. With pipe threads I get a more compact setup.
 

I decided to add a pressure regulator too so I can run the electric pump all the time if needed.

I'm not sure where this mounts or what your physical constraints are as far as locating components, so I understand that there can be inefficiencies as a result. What are the fittings on the pump? NPT? The advantage to bending a hard line is that you could avoid the extra elbows on either side of the pump and just use a pair of L-shaped hard lines. The other question that comes to mind is, can this pump be drawn through when it isn't running? Some electric pumps can just be mounted in line and the mechanical pump can pull fuel right through a non-operating electric. A diaphragm electric would be like that. Not sure about a rotary pump. It would save a lot of effort.

[Stude Light]

This pump is able to be drawn through and I’ve been using it that way but I wanted to eliminate all possible restrictions in the fuel supply line to reduce possibility of vapor lock. Yes, it’s overkill.

[68LTD]

Couple of thoughts, why still use the mech pump??  Your return line goes back to the feed line from the tank, would it be better to have its own tube back into the filler neck or top of tank, with some small restriction to maintain good supply to carb. ??   I have installed some 8 red Holley pumps without return line, no issues, but these have been on 1955 and newer v8's, none use the mech pump.  All have clear filter near carb to see if fuel is indeed in the line. 

[Matt Harwood]

This is the fuel pump setup on my '35 Lincoln, including bypass and check valve. Fittings are all single flare, as original.

 

[Stude Light]

15 minutes ago, Matt Harwood said:

This is the fuel pump setup on my '35 Lincoln, including bypass and check valve. Fittings are all single flare, as original.

 

Thanks Matt. That looks like a pretty clean setup and I see the pump is double isolated. It doesn’t look like you run a regulator on your Carter pump. What is the max psi on that? I need to stay below 3 psi so I’m thinking I need a regulator even with the pump I have. I never thought about it but I assume you can pull through a regulator. 
 

That rotary vane is probably better than the solenoid style on my car…I have the option to change it.

 

My LaSalle uses double flare 3/8” fuel line. I tried flaring those original steel lines with my double flare tool with poor success so I pulled the original lines off the car today. I will be replacing those with modern lines. 
 

Primarily, I just wanted to hard pipe the pump but then I thought about adding a bypass even though not really needed with the solenoid pump but I thought it may help reduce restriction. This simple project keeps expanding….

[Pont 46]

Hello I plan on doing this same thing with my 46 Pontiac, if you dont mind me asking asking. What is the need for the by pass line? Can i just right the fuel pump without by pass? Where does  check go?

 

thanks for sharing your knowledge

[Robert G. Smits]

I have used a inline rotary pump at the tank without bypass on my 41 Cadillac for 16 years and thousands of touring miles.  Only used for starting and occasional vapor lock.  I think you are making this too complex.

[Stude Light]

9 hours ago, Robert G. Smits said:

I have used a inline rotary pump at the tank without bypass on my 41 Cadillac for 16 years and thousands of touring miles.  Only used for starting and occasional vapor lock.  I think you are making this too complex.

You are right about too complex. I get frustrated sometimes with the car vapor locking so I was going to throw everything at it.
 

I picked up some new fuel line and I’m just going to hard plumb my old pump setup and start using rec fuel. That will get me 90% there.

 

I thought I would also try ducting a little cool air right over the fuel pump to see if that helps some. There is a small area between the radiator and sheet metal I can grab some cool air

Then blow over the pump 

It can’t hurt to try.

 

 

 

Edited June 6, 2023 by Stude Light (see edit history)

[Stude Light]

9 hours ago, Pont 46 said:

Hello I plan on doing this same thing with my 46 Pontiac, if you dont mind me asking asking. What is the need for the by pass line? Can i just right the fuel pump without by pass? Where does  check go?

 

thanks for sharing your knowledge

If you use the pump setup that I have then there really isn’t a need for a bypass. That was me just being a bit retentive about things.

 

If you use the pump setup that Matt has then you’ll need a bypass as that unit you can’t draw through when the pump is off.

 

Most of us just use an easily reachable switch to run the pump just before starting to fill the float bowl or compress the vapor out of the fuel when we get vapor lock. I rely on my mechanical pump to run the car. No better way to burn your car up than with an add on electric pump that is poorly designed, installed or used incorrectly.

Edited June 6, 2023 by Stude Light (see edit history)

[Pont 46]

Thanks Stude

I am using the same type of fuel pump as you. I also going to set up a hidden switch , I am mounting mine right near tank, with a 100 micron fuel filter first before pump. I dont need this pump to start car, just a precaution if my fuel pump goes out on a trip.  Yes agree last thing I want is a car fire, 

 

Sorry to hear about your problems with vapor lock, very frustrating.

If I was closer I would come over and help you install pump. 

 

 

[Bloo]

Something like a screen at the pump inlet would be more appropriate than a fine filter if you have a vane or roller pump, and I think you do if it's like Stude Light's picture. They don't like to lift and they don't like any restriction on the input port. It is already going to be unhappy about having to lift the fuel out the top of the tank. They cavitate. On the other hand if the pump is s thumper, it probably won't care.

 

I'd put a sock on the fuel pickup and forget an inlet filter altogether. The pump isn't going to like that either, but it is probably less bad.

 

Edited June 6, 2023 by Bloo (see edit history)

[Gary W]

I installed a 6V electric pump to simply prime the carburetor after the car ('37 Buick) has sat for about a week.   The fuel in the bowl would evaporate, so instead of running the starter motor over and over to prime, now the electric pump, installed inline, does the job in about 30 seconds.  

 

Here is the entire write up:

 

 

[keithb7]

I went with this set up. Works great in my ‘38 Chrysler. Hopefully there is something valuable here. 
 

https://youtu.be/d2pQW_LIdiE

 

[Stude Light]

@Gary W, that one way valve is actually a fuel filter.

@keithb7, I had to laugh when you mentioned the cut brake line. We have all been there at one time or another 😀

[Stude Light]

I appreciate all the input. I decided to simplify the project to just hard piping the setup I had and adding a pressure regulator so if I need to run the pump more often, it won’t over power the carburetor needle and seat. It is set to 2.8 psi.

 

I replaced the original fuel lines from fuel tank to engine, used the original asphalt cloth style insulation where required and I pre painted everything flat black to blend in (and it’s easier to spot a leak).

This regulator has a second outlet (pointed straight down) that can be used as a drain to pump the fuel out of the tank if ever required.

 

I also switched to ethanol free fuel to help with the vapor lock issue. Hopefully that and my fuel pump cooling duct will solve any vapor lock issues. I won’t really know until I drive it longer distances on a hot day but I have a reliable solution if needed that doesn’t have any rubber lines and screw clamps.

 

Side note - I enjoy driving my prewar cars as it takes a bit more skill and planning but the downside of the LaSalle is it drives nicer than most 1960s cars.

 

[Marty Roth]

On 6/6/2023 at 12:27 PM, Stude Light said:

If you use the pump setup that I have then there really isn’t a need for a bypass. That was me just being a bit retentive about things.

 

If you use the pump setup that Matt has then you’ll need a bypass as that unit you can’t draw through when the pump is off.

 

Most of us just use an easily reachable switch to run the pump just before starting to fill the float bowl or compress the vapor out of the fuel when we get vapor lock. I rely on my mechanical pump to run the car. No better way to burn your car up than with an add on electric pump that is poorly designed, installed or used incorrectly.

Absolutely disagree-

@Robert G. Smits  and I have used the same rotary vane 6-Volt Carter P4259 for well over 16 years without the need for a bypass. The mechanical pump on my '41 Cadillac and the '37 Buick Roadmaster (331 cu in and 320 cu in ) pull just fine through the non-running electric pump. The Carter Electric is energized only if and when the car has been stored for an extended period, or in the case of vapor lock, to which these cars are prone, especially on modern fuels. For the '30 Packard I added a Holley Pressure Regulator

[Stude Light]

2 hours ago, Marty Roth said:

Absolutely disagree-

@Robert G. Smits  and I have used the same rotary vane 6-Volt Carter P4259 for well over 16 years without the need for a bypass. The mechanical pump on my '41 Cadillac and the '37 Buick Roadmaster (331 cu in and 320 cu in ) pull just fine through the non-running electric pump. The Carter Electric is energized only if and when the car has been stored for an extended period, or in the case of vapor lock, to which these cars are prone, especially on modern fuels. For the '30 Packard I added a Holley Pressure Regulator

My experience with the Carter pump is with two cars that had a Carter pump installed already (by others) and both had a bypass installed. That along with several on this forum that had a similar setup.

 

If you have personal experience with a Carter without a bypass, I stand corrected. I wonder if there are different Carter designs which would have caused others to add a bypass?

 

I added the Holley regulator to my setup since my pump can put out 7 psi  and my carb is only good for about 3 psi.

[Dennis Hagen]

I have a electric fuel pump on my 51 Buick in Az, helped for vapor lock while driving but what also helped I mounted a 4” blower ( like is used to evacuate engine compartment on inboard boats before startup) inside left front fender well with flexible metal duct to bring cooler air to blow over carb. That works well while sitting at long lights or after shutdown. I have a timer on it so you can park and walk away  and restart after 15 minutes.

The carb sits right on top of the exhaust manifold on straight eights.

 I have since installed efi on that car that solved the problem but I know some of you want to keep your car as stock as possible but the desert heat gave me any choice.

[Dave39MD]

I looked at the instructions of a P 4259 Carter I have in stock and it says it should never be used as a booster pump with the mechanical pump in place, it should always be used separately. I want to use it on my Buick and now I am not sure since I want to keep the mechanical pump.

 

Dave

[Stude Light]

Most of us just use these for starting and do not leave them on for driving.
 

I’m sure the lawyers at Carter want to avoid any potential liability from people that have failed mechanical fuel pumps. If you have a failed diaphragm, the electric pump will push fuel through that hole in the diaphragm which may end up in the engine or engine compartment. If you use your mechanical pump for all but starting you will know if you have a bad mechanical pump and you will not want to run your car with the electric pump which minimizes any risk.

[28 Chrysler]

Have a switch for the pump that is on the switched circuit for the ignition.

The second switch could be a toggle on the bottom edge of the dash.