I've got generator fuel that might sit for 2 years or so before I pour it into a car to get rid of it. It's when it sits in a carburetor it causes issues. Older ignition systems with points are a little more temperamental.

Electric pumps push. Mechanical pumps pull. A vapor bubble will expand when pulled and cause locking when it hits the pump and just sit there quivering. An electric pump pushes and the vapor bubble will burp inside the carburetor and go out the vent bowl.

Carbureted engines usually run around 6-7 psi. Non-race pumps are often set to that pressure.

 

The flatheads are bad because of the way the fuel lines are routed. ... V8's you have better options for routing.


What is common is to be driving down the highway and have no problems, then pull into town in stop and go traffic and the engine bay heats up more, your not using much fuel and it just sits in the line and heats up .... modern fuels have a lower boiling point then older fuels ....this was not a problem with past fuels ... as it heats up it turns from a liquid to a vapor.
The fuel pump will not push vapor and the engine runs out of fuel and dies .... will not start again until it cools down.

Same thing happens if you shut the car off and run into the store for 5 minutes and come back out and car will not start because of heat soak with the cooling system off and rising temps ... you have 20 minute for it to cool off before it will start again.
Electric pump will help with these situations and they sell electric fuel pumps that push 3-5 psi and even have them in 6V for older vehicles.

Modern vehicles do not have a problem because they have electric pumps and a return line back to the tank, so there is always fresh cool fuel circulating.
Some say that adding a return line to our old vehicles will help prevent the problem from happening.
While a electric pump helps, it does not prevent it from happening.

Not every vehicle will have a problem, it is a common issue on older cars though .... your climate and driving habits play a big part.
Usually here in Texas will be 110 degrees out this time of year .... plus engine heat in the engine bay.
ASTM specifications define gasoline as having a boiling range from 122-158°

Just things I think about with a 57 Dodge fuel system.

 

Regardless of what you use mechanical or electric the fuel is heating up near the motor. It will start to boil which causes vapor lock. Keep the heat away from the fuel lines and not have to deal with it in the first place is the way to go. That fuel line is way to close to the exhaust! They should have ran it up front then down to the pump. Installing fuel line insulation is another way to keep the heat out.

 

You are not wrong .... regardless of what we think ... back then there was no issue to fix .... As they keep improving the fuel, old cars have a problem.
Then the carburetor intake manifold is bolted to the exhaust manifold ..... is why heat soak and the extra 30 degree temp rise will affect it when you shut the engine off.


Back in the early days, some cars just ran a filter like this to keep the fuel flowing ... large end to the carb and small end to the tank .... if the float closed, the excess just went back to the tank .... just a constant supply of cool fuel.

Now in my case I can not use this method, requires rubber fuel lines above exhaust manifold. .... possibly a 57 V8 can run this filter.
I have a plan! .... I'm thinking of a brass T in front of the fuel filter and a smaller metal line going back to the tank.

Everybody that runs into this issue with any older car just runs a electric pump.
IMHO, the vapor lock puts you into the ditch .... the electric pump gets you out of the ditch.

What if you ran a recirculating fuel line and never got put in the ditch in the first place?
By having the fuel recirculating in the first place will keep the fuel cooler .... when you shut the engine off at the gas station, heat soak will not matter because the fuel was cooler in the first place.

Just notice my advice to the poster was to just install a electric pump.
Anyone I talk to about the problem .... just not interested ... they know electric pumps just fix it. and they already have them installed ... been there and done that, not going back.

So I'm the only one that wants to perform this experiment.
First thing I want to experience vapor lock and know I have the issue.
Then I want to install the return line and see if it goes away or even helps.
Then when I made the new existing fuel line, I installed a fuel filter where the future electric pump will go.
I kinda already suspect I will need a electric pump .... I just want to try first.