1955 vapor lock symptoms

[OlleHi]

We had around 30 degrees Celsius (86F) in sweden (Hot for being here!) last week when I was out driving. After 30 min the car started to run quite bad, like out of gas. And misfiring.
When I checked the fuel filter it was empty. I suspected vapor lock or maybe the fuel pump. After a while I started it up again, I could se that some bubbles came with the fuel, and it ran for 5 minutes, so it took a while to get home again!
The car was restored 2018-2022, but not the engine. I replaced the fuel pump 10 years ago.
Today when it was around 25 degrees Celsius (77F) I drove and same thing happened again a couple of times. But I only drove maybe 10 minutes before the first stop.
Can it be something with the fuel pump? I opened the gas cap to see if it made any sound, like the tank wasn't vented. You know the pffft sound?
But if something is wrong with the fuelpump, the car wouldn't start again, would it? Is there anything I can check in the fuelpump?

Thanks!
Olle, Sweden

This page contains affiliate links for which I may be compensated. As an eBay Partner, and Amazon Associate I may be compensated if you make a purchase at no cost to you.

 

[biddle]

Discussed here-

Thread 'Vapor lock problem on a 1956'

Jul 19, 2021

I've run into a problem that has me scratching my head. I've rebuilt my car from the front to the rear and it has run fine for around 1,000 miles over two years. I have electronic ignition, Holley 1841 carb, 312 with auto. The other day I got about 10 miles from home driving on surface streets and all of a sudden the car started running rough. I got turned around and headed home with the car only able to run around 30 mph. At no time did it backfire just wouldn't run but if I gave it a accel pump shot the motor would pick up and then die back down. So I'm thinking that I have a fuel pump...

• ron56
• Replies: 52
• Forum: 1955 - 1966 Classic Ford Thunderbird

 

[59tbirddavid]

Your motor is starving for fuel, fuel filter is first place to look.

 

[Ronl2025]

The same thing happens on my '61 when the temp goes into the upper 70's. I'm going with vapor lock. I'll bet the fuel pump and filter are fine. Classic engines tend to run hotter than modern cars — smaller radiators and less efficient airflow, everything is steel, which has great heat retention. Great for home radiators, but in classic cars not so much. Plus the boiling point on today's fuel is a lot lower than it was pre-1980, and with the addition of ethanol, the boiling point is even lower. I only use ethanol free gas (which didn't solve the problem anyway), did change the fuel pump, added a 1" phenolic plate under the carb, and the gas cap IS vented, also tried heat shield wrap...no luck. You could just drive in the Spring or Fall, but that's no fun, ya miss too much drive time, and I don't have the problem in lower temps. Been stuck twice, because of vapor lock, with my granddaughter in the car, also not a great time, and had to sit for 2.5hrs for the car to cool. So, the bottom line, today I picked up the last 2 pieces needed to install an electric fuel pump. Although it obviously isn't my first choice, I now have my weekend project. I know this will definitely solve the problem. Good luck!!

 

[Tom Alpers]

Could be vapor lock but at such mild temperatures I would mostly suspect that the fuel pump isn't doing too great. Since the fuel pump is 10 years old I would have it rebuilt as a start. Small electrical fuel pump kits are less than $100 and in my view worth adding for the peace of mind. When I first got my car I had to use the elecdtric almost all the time. Had the mechanical rebult by Aurther Gould 3 years ago and have not needed the electric since.

 

[pltmgr]

Make sure your gas cap is vented and working. Insulate your fuel lines. Check out your fuel pump for proper operation. Use ethanol free gas. Consider adding a return fuel line to your gas tank. Electric fuel pump is another option. Very common problem with todays gas that is formulated for fuel injection, not carbs.

 

[Texas TBird]

This worked for my 55: (and I'm in a hot Texas area)
. install 3 way inline fuel filter with return line to gas tank (I used the drain plug in the tank for the return)
. install inexpensive electric fuel pump near the tank to run in conjunction with your mechanical one. (I put a switch under dash, but rarely turn it off)
. use only ethanol free gas

Can't really say which of the three fixed the problem as I did all three at the same time. Good luck!

 

[doug7740]

We had around 30 degrees Celsius (86F) in sweden (Hot for being here!) last week when I was out driving. After 30 min the car started to run quite bad, like out of gas. And misfiring.
When I checked the fuel filter it was empty. I suspected vapor lock or maybe the fuel pump. After a while I started it up again, I could se that some bubbles came with the fuel, and it ran for 5 minutes, so it took a while to get home again!
The car was restored 2018-2022, but not the engine. I replaced the fuel pump 10 years ago.
Today when it was around 25 degrees Celsius (77F) I drove and same thing happened again a couple of times. But I only drove maybe 10 minutes before the first stop.
Can it be something with the fuel pump? I opened the gas cap to see if it made any sound, like the tank wasn't vented. You know the pffft sound?
But if something is wrong with the fuelpump, the car wouldn't start again, would it? Is there anything I can check in the fuelpump?

Thanks!
Olle, Sweden

From what you are describing it sounds like a fuel delivery issue. Start by performing a fuel pressure and volume test. According to the service manual, the fuel pump pressure specification is 4.0 to 5.0 psi at 900 rpm and the volume specification is 1 pint in less than 45 seconds at 900 rpm.

Your car has two "filters" which attempt to remove debris from your fuel before it enters your carburetor. The first filter is the one in the glass bowl located in the fuel line as it makes its way from the fuel pump to the carburetor. The second "filter" is the one that is most often overlooked and forgotten. If you have changed your fuel filter recently, yet your car still suffers from poor acceleration, your problem may be a clogged fuel screen. This screen is located behind the brass fitting which connects your fuel line to the carburetor.

To clean your fuel screen, you first must remove the fuel line from the brass fitting. On 1955 and 1956 Thunderbird's the fuel line should go to the back of the carburetor. Once the fuel line has been removed, unscrew the brass fitting from the body of the carburetor. There will be a gasket attached to the brass fitting. This gasket must be reinstalled behind the brass fitting, or your car will be leaking fuel. Inside the brass fitting will be a wire screen. This is your fuel screen. You can tap it out of the brass housing. Inspect the screen for sediment buildup. Your screen can be cleaned with carburetor cleaner. If your screen is bent or missing, you will need to order a replacement screen. Once your screen has been cleaned or replaced, reinstall the fuel screen back inside the brass housing. Reattach the brass housing to the carburetor. Do not forget to reinstall the gasket. Once you have installed the brass housing reconnect the fuel line. If your screen was clogged, you should notice a definite improvement in your car's performance.

The gas cap on your T-Bird must be vented to allow air to enter the tank. If air cannot get into the tank vacuum will be created which can stop the flow of fuel to your engine.

Last summer, I had to replace my gas cap, and I discovered that when I removed the gas cap after running the engine for a while, I could hear the sound of air rushing into the tank. To vent the fuel tank, the 1955 and 1956 gas caps have a rib stamped into the surface which allows air to enter from the outside edge of the cap to the center. The problem with my gas cap was that the inside diameter of the gasket was so small that it prevented the venting process.

The problem was easily fixed by removing the gasket from the gas cap and increasing the inside diameter of the gasket by cutting it with a razor blade.

doug7740
1955 Thunderbird Blue