How do you stop vapor lock?

ajohn

ajohn

Senior Member
My 30 A is highly modified with header, Thomas head, inserted, pressurized rods and mains, synchromesh trans, 4 wheel disc brakes, weber 2 barrel downdraft carb. It vapor locks big time on a hot day in traffic, It had an electric fuel pump that it appears to do better without with a rubber gas hose from the firewall fuel filter to carb. I have been advised to buy aviation gas. Any thoughts or suggestions? Ajohn
 

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In the photo, you can see the gas line near the header and the electric pump that was on the frame. It now has a rubber line from the fuel bowl on the firewall to the carb, away from the header. Ajohn.
 
With an electric fuel pump, vapor lock shouldnt be a problem. You should try non-ethanol gas if you can, but I doubt that is all your problem.
What sort of ignition components are you using?
 
You could try re routing your copper line, etc . I run two wooden cloths pegs on the fuel line , Sure it don,t work but since doing it & others , no more vapour locks , plus on a tour wife can peg the washing out . so you get two for the price of one , Keep the salt dry .
 
In the past when I had vapor lock, I would use premium gas and the problem would go away. But like said before, you should really be experiencing vapor lock with a fuel pump. I never had since adding one.
 
try taking the fuel line up and over header pipe one. or try sliding a larger rubber hose over the copper by the header. keep the heat down.
 
Some on this forum have suggested Marvel Mystery Oil as a possible cure to Vapor Lock.
Rubber Hoses and clothes pins on the fuel line have also been mentioned.
 
Didn't they us a raw potato or two on the copper lines in the "day/" I insulated mine with some aluminum foil when I drove to Texas in the summer. That seemed to help a bit. Loosely wrop the line and tape it so it won't blow away, I had a waffle pattern manifold without the heater so it cooked anything close to it. Headers should be shielded from the gas line on hot days, in my opinion, for whatever that is worth.
 
move the fuel line as far away from the exhaust pipe as you can, make a heat shield out of aluminum or thin sheet metal and attach it to your fuel line between it and the exhaust using spacers on the fuel line
 
Wrap your header with DEI thermo tape. Keeps heat in the pipes where it needs to stay.
Performance will improve, should keep heat away from your fuel system
 
Old time fix used back in the day was to put a heatsink on your fuel line, (I remember my Dad and Uncles doing this)
Heatsink=wood clothpins
But like other have said...get away from the corn gas, if at all possible.
 
On one of our Summer Tours we had a whole bunch of Model As have vapor locking problems. The one that didn't was using ATF in his fuel, it is very similar to Marvel Mystery Oil but cheaper.
 
I wish someone would explain the science behind the clothespins. Wood is not a good conductor of heat. Science tells me that air is a much better insulator and therefore, a loosely attached sleeve of tin foil with air between it and the gas line is much better. I think the clothespin idea is smoke and mirrors. Hear come the slings and arrows...

Frank
 
When I attended the high country tour in Breckenridge a few years ago, they had a seminar on remedies to prevent vapor lock and other problems experienced driving our Model A's at high altitude. Besides some of suggestions already mentioned, one of the suggestions I have incorporated is to get an oven door gasket, slit it length-wise, slip it over the gas line, and secure it with zip ties. The goal is to try to keep the gas from boiling which I'm sure it can do on those hot Texas days.
 
I should have said this before but it just came back into my mind. A guy had the luck of his 80s chevy one ton stalled out in front of my dads cabin while i was working in the yard. i knew when i heard the sound . he was out of gas they seem to get a certain sound when out of fuel. we get some gas back in and it still wont go. It was a JUNK fuel pump on top of running out of gas. we got the gas back in but the pump being a cheap autozone electric. would pump fuel but didnt have the power to pump the air out of the line from the tank to the carb. I had to manuely help the fuel up the line. moral of the story and in caps so its easy to pick out of the book im writing here: CHECK THAT YOUR FUEL PUMP IS IN GOOD WORKING ORDER. ALL THIS COULD HAVE BEEN CAUSED FROM A LOW QUALITY PUMP BEING WORE OUT. it also may have been corn gas that wore his pump out.
 
header pipe too close to bottom of carb causing gas in float bowl to boil is what my thoughts are from the pics
take a piece of tin cut a couple slots in it so you can get a hose clamp thru and clamp it to the header pipe under the float bowl
it's worth a cheap try
used to have do do that back in the day with a high performance street/ drag race car

good luck
Terry
 
Maybe check the float level. A small amount of fuel in the bowl may boil.

The only time I've seen what may have been "vapor lock" was after fitting a Webber like that (not to a Model A).
 
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