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Old 06-23-2019, 03:26 PM   #1
ktgarcia
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Default Vapor lock question

I have contacted some FordBarn members and read most of the comments about installing an electric fuel pump to compensate for the vapor lock that can occur while using just the mechanical fuel pump.

Some members say to install a relay. Some have said to wire the electric to a toggle switch and others have said wiring it to the ignition switch so you don’t forget to turn off the toggle and run the battery down.

With the installation of a toggle switch, I assume (you know what that means) you leave the manual pump in place. Some of you members have said you need to gut the mechanical leaving the push rod and just use the electric to avoid the vapor lock problem. Others have commented that they use the electrical pump to override the mechanical pump when the vapor lock occurs or after sitting.

With so many different solutions that members have done and been successful, I am trying to sort them all out and use the best solution for solving my vapor lock problem.

I am thinking of putting an electric pump near the gas tank, wiring it to a relay through the ignition switch, and leaving the mechanical pump in place. If there is something wrong with my thinking I would appreciate any additional comments that members might have.

Thanks to all of you that have responded to me and others who have added their comments on the Forum.

I just wonder if the mechanical pump can’t keep vapor lock from occurring, then how can the electric pump ‘push’ gas through the mechanical pump to compensate for the vapor lock that has occurred at the carburetor.

Any suggestions or corrections to my thinking will be helpful.
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Old 06-23-2019, 03:49 PM   #2
corvette8n
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Default Re: Vapor lock question

My electric pump was installed by the previous owner, it's a pull thru type, mechanical pump is still in place. I have a spring loaded toggle switch sticking straight down from the dash, I hold the switch on until I hear the pump noise change, when I let go the electric pump shuts off, car then starts fine. I haven't had it vapor lock on me yet. Switch also wired through ignition. Hope this helps.
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Old 06-23-2019, 03:57 PM   #3
JSeery
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Default Re: Vapor lock question

Vapor lock occurs when liquid fuel vaporizes. Many things can contribute to fuel vaporizing. Both heat and pressure come into play. High heat can boil the fuel in the carb float bowl (vaporize it). Low pressure on fuel can also vaporize it. The higher the pump is relative to the fuel tank and the futher it is away from the tank the lower the surface pressure on the fuel will be. That is because the pump pulls the fuel by creating a lower pressure at the pump relative to the tank. This increases the likelyhood of vaporizing the fuel. A pump mounted low and near the tank requires much less pressure drop between the tank and the pump and pushes the fuel under pressure to the carb.

Last edited by JSeery; 06-23-2019 at 05:47 PM.
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Old 06-23-2019, 04:01 PM   #4
donald1950
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Default Re: Vapor lock question

i have used AirTex pull through fuel pumps and used a off / momentary on switch to prime the carb after the car sat for a while. have never experienced vapor lock. do not gut the stock fuel pump. use the momentary on switch prime the carb and that will also help the stock fuel pump. install the electric pump as close to the gas tank as possible. Stromberg and Holly carbs may not like the 4 PSI pressure of the electric if you choose to run one full time so you may need an adjustable pressure regulator set for approx
2 PSI.
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Old 06-23-2019, 04:02 PM   #5
JSeery
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Default Re: Vapor lock question

Running the amperage an electrical fuel pump requires through the stock ignition switch is not a good idea. It was never designed to carry much of a load.

Last edited by JSeery; 06-23-2019 at 05:44 PM.
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Old 06-23-2019, 05:21 PM   #6
drolston
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Default Re: Vapor lock question

I had bad vapor lock problems on hot days. It would starve for gas, even while driving. With clear fuel lines from the mechanical pump to the carburetor, you could see the vapor bubbles in the fuel line. I have all accessories wired through a separate switch so all that current for the radio, GPS, electric fuel pump, etc., does not go through the ignition switch. My fuel pump switch has momentary position for priming after sitting, and "on" function for driving in traffic on hot days. The electric pump makes enough noise that I do not worry about leaving it on when I park the car.

When bubbles form before or in the mechanical fuel pump it will not pump very well because when the push rod causes the diaphragm in the pump to squeeze in on the chamber inside the pump, the vapor compresses and does not raise the pressure enough to move vapor out. When liquid fuel is in the chamber, it can not compress, and as the diaphragm squeezes into the chamber, fluid gas is forced out to the carburetor. As JSeery explained, the electric pump is in a location that is much less likely for fuel to vaporize. Both mechanical and electric pump will move vapor, but the electric pump is much more efficient with vapor. If you ever ran your flathead out of gas you always poured some gas in the carb to get it started, because you could easily kill the battery cranking to get the mechanical pump to fill the carb.
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Old 06-23-2019, 07:24 PM   #7
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Default Re: Vapor lock question

I run the original type mechanical pump, backed up by a Facet self regulating pump made by Purolater in NY, USA. I run a wire from the fuse block to a toggle switch under the dash, through a green on light on the dash to the pump. The light is on when the pump is on, plus I can hear it change pitch when the pump is primed. I use it only for priming the mechanical pump, and as backup. No vapor lock experience in that car. Facet pumps are reasonably priced, about $35,, with various options for the GPM and pressure you want. Carried by Aircraft & Spruce, used for experimental aircraft if that tells you anything about the reliability.
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Old 06-24-2019, 01:38 PM   #8
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Default Re: Vapor lock question

I run an airtex electrical fuel pump and the stock mechanical pump,i use the airtex to prime the carb then turn it off,i use phenolic spacers and I have never had vapor lock.If the mechanical pumps fails on the road I can get home with the electrical
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Old 06-24-2019, 02:54 PM   #9
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Default Re: Vapor lock question

More often than not, "vapor lock" is due to a weak ignition coil. As the coil temperature increases, resistance goes up, and current goes down (Ohm's Law). We leave the stock pump in place and use the electric pump to top off the carb after a long storage, or the evaporation due to heat soak when a hot engine is shut down. I use a regular toggle switch for he electric pump (an Airtex) wired to the accessory post of the stock ignition switch. This way, the pump is disconnected when the car isn't being used, and if you have a spring switch, and need the electric pump to get home, you don't have to drive with one hand on the switch. This setup,on my '47 has been trouble free for the 25 years of owning the car.
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Old 07-05-2019, 07:23 AM   #10
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Default Re: Vapor lock question

Have a similar setup in my 47 monarch installed by previous owner .I only use the electric pump occasionally when car has sat for a few days or it is very hot out .
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Old 07-07-2019, 10:19 AM   #11
grumppyoldman
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Default Re: Vapor lock question

I just removed the mechanical pump on my 41 and installed an airtex electricpump back at the tank. What problems am I likley to have with this set-up. Al
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Old 07-07-2019, 06:47 PM   #12
drolston
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Default Re: Vapor lock question

Quote:
Originally Posted by grumppyoldman View Post
I just removed the mechanical pump on my 41 and installed an airtex electricpump back at the tank. What problems am I likley to have with this set-up. Al
Likely? None.
But I carry a spare electric fuel pump. And a spare distributor, and coil. That should take care of about 75% of breakdowns.
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Old 07-07-2019, 08:01 PM   #13
RalphG
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Default Re: Vapor lock question

I recall my dad talking about vapor lock occasionally on the 52 Merc when it was his daily driver in the 1960s. Maybe today's gas is less subject to it but in the 4 years I have had the Merc back in service it has never vapor locked. Came close one hot August day leaving a car show but it turned out to be a leak at the sediment bowl gasket on the pump. Tightened it up and it has been fine since. (But I do carry a new gasket in the glove compartment).
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Old 07-07-2019, 11:21 PM   #14
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Default Re: Vapor lock question

Ralph even in Florida I didn't experience it. I did experience coil fail but resolved it with skip.


I never run anything less then no eth.



I did have a starting issue recently. Pumped the accelerator after a run before cranking it.... Never had a issue before. Cranked it with accelerator to the floor and it started up, did 5 miles. Guess it was loaded up (flooded). Shouldn't have pumped it I guess.


We all have cool startup procedures.


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Old 07-08-2019, 10:59 AM   #15
grumppyoldman
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Default Re: Vapor lock question

I've noticed since the electric pump installation, the fuel pressure gauge holds at 2 lbs. without the pump running. Engine fires up quicker than before. Al
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