Vapor lock

[BobDeSoto]

My understanding of vapor lock is that the fuel is boiling in the line probably because the fuel line is too close to the exhaust manifold.

 

I don't think the weather would matter.

 

I've had vapor lock occur after I have coasted down a city street - not using any gas - so the gas in the line hasn't moved as

much as if I have been on the gas.  After I've stopped at the light/stop sign the car stumbles when it is time to go.  Runs fine

an hour later.

 

 

[TodFitch]

There seems to be two issues related to fuel volatility:

1. Expansion in the carburetor float bowl when parked hot causing some fuel to get into the manifold "flooding" it resulting in a hard to start situation. I haven’t had this but the initial work around is to hold the throttle wide open (no pumping) when starting and/or lowering the float setting a little bit.
2. Fuel vaporizing in the fuel pump. The pump is not as good at pumping vapor as it is fuel so the carburetor is starved for gas. This usually happens when parked hot but can also happen on hot days when idling and there is not a lot of airflow past the fuel pump. At least for some years the factory added a heat shield between the exhaust manifold and the fuel pump to reduce this issue. Another thing one can do is add an electric fuel pump near the tank, often on a momentary switch to be used in these cases or for priming the carburetor if the car has been parked for a long time.

[keithb7]

Vapor lock solutions in 50 words or less:

 

1. Non-ethanol Fuel

2. 6V Electric Priming Pump w/toggle switch

3. Fuel pump heat shield

4. Thin metal base plate at carb base

5. Phenolic spacer adaptor at carb base

 

Two other options I have not tried: Heat shield around fuel lines. Cloths pins, I simply refuse to try this.

 

Edited March 6, 2022 by keithb7

[Los_Control]

I think I would try Uncle Tony's trick for vapor lock if I run into the issue.

Simply adding a fuel filter that has a 2nd outlet to return to the tank, has a flow resistor built into it. This would also mean modifying the tank to add a port for the fuel to return through. Several ways to do this. My Tank has never been installed or gas in it. I have a extra plate on it for a electric fuel pump if wanted. Would be very simple to add it there before installing the tank.

 

The whole idea is the fuel is always moving so never sits in the line long enough to boil over. Since it is already cooler, seems it wont boil over when shutting the engine off.

The restriction built into the filter return line will keep you from starving for fuel.

iirc some jeeps used the filters & available at any parts store. Some put the restriction at the tank some at the filter, you need the restriction so important which filter you buy.

 

IMHO, will look sorta kinda tacky. Will need to add the filter after the fuel pump, they accept rubber fuel lines. Simple easy fix though.

 

I wonder if a guy was handy, might take his steel or nickel/copper fuel line and just add a T before the carburetor And run metal lines back to the tank.

You can blank off whatever fitting going into the tank, just drill a small hole for flow restriction. I wonder if the flow restrictors used on brake lines is fuel friendly?

Would look more period correct this way at least.

 

 

[Happy 46R]

I use both the heat shield on the fuel pump and a heat shield on the after market fuel filter that was added just before the carburetor. I have had one issue of vapor lock and the outside temp was 32 degrees Celsius and the car had been driven for about 2 hours at less than 30 mph (caravan) and then let sit for about an hour. As  mentioned as soon as I started to crank the engine and it didn't want to catch. Foot to the floor and within 20 seconds it fired, spit out some smoke and then settled into sinus rhythm.  My original car as a kid had a wooden clothes pin on the fuel line just before the carburetor and despite the high temperatures in Penticton I had no troubles with vapor lock. Here are pictures of the after market (read as home built) shield someone made for the fuel filter (lower left edge of picture) and the factory added fuel pump shield which is the sideways S shape immediately below the exhaust manifold and immediately above the fuel pump mount. 

[Sniper]

The critical piece of information UT didn't mention

 

3/8" hard line, 1/4" return (discontinued, but some availability)

 

NAPA 3041

Wix 33041

 

5/16" hard line, 1/4" return no orifice

 

NAPA 6040

Wix 33040

[1949 Wraith]

I chased a vapour lock problem on one of my trucks. Had the guards, primer pump, etc. Ended up the diaphram in the mechanical fuel pump was begining to fail.