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Old 03-20-2015, 09:50 PM   #21
steve s
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Default Re: Fuel line shield to prevent vapor lock?



Here's picture of fuel vaporization in progress. The silvery area in the top of the sedimentation bowl is a bubble of vaporized gasoline. With the motor idling on a warm day, I could watch the bubble grow until it filled the screen surface, then the whole thing would burp out and down the fuel line, and the process start over again. The engine barely hiccupped when the bubble passed thru.

Under harder running, hotter conditions, this sort of thing can happen in the line, carburetor, and any fuel filter that may have been added, which MIGHT then shut down the motor.




Here's a picture of some straws I grasped at to fight vapor lock: fiberglass and reflective coating on sed. bowl, and aluminized duct tape over rubber fuel line over metal fuel line. It helped a bit.




Here's a heat shield a buddy made and gave me after he timed his engine and didn't need it any more.



Here's what was the final solution for me.

Ethanol aggravates vapor lock by what's called non-ideal mixing with gasoline of the positive deviation from Raoult's Law kind. It raises the vapor pressure of the most volatile gasoline components beyond what it would be in pure gasoline--the ethanol doesn't itself vaporize particularly easily, but it causes the gasoline to vaporize more readily than normal. The problem is further aggravated when winter blend gasoline is used in warm weather. THey don't have winter blend down south, so, paradoxically, vapor lock is less of a problem in places where it's never very cold.
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Old 03-20-2015, 10:27 PM   #22
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Default Re: Fuel line shield to prevent vapor lock?

We have seen videos and pictures of the problem, but it is not a thing that happens to all or even most stock Model A's. Here in Florida I know of no one in our club that has or even had this problem.

Hot temps - we have that in Florida
Slow driving - we have parades here in Florida
"Corn" gas - we have that in Florida

I'm not saying it does not exist. A search of this site will show "vapor lock" to be in the top ten or maybe top 5 problems.


For every cause there is a logical reason why that can't be the problem. Anybody that does troubleshooting for a living will tell you you need to find the cause before you can solve the problem. In this case we can only chase the symptoms.

All the "solutions" above have worked for some but not for all. Keep doing different things until you find a solution that works for you. Let me add one, some one made a non metallic spacer that went between the carb and the manifold and his problem went away.

Nothing is more frustrating then a fairly common problem with no exact cause or solution.
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Old 03-20-2015, 11:20 PM   #23
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Default Re: Fuel line shield to prevent vapor lock?

No picture. I had a waffle manifold without the cover to take the heat into the cab, so that waffle is a large block of hot metal close to the distributor and not too far from the carb. I took some alum. foil and folded it several times and put it between the manifold and the carb.I had been replacing the condensers pretty often to keep running and when I put the foil in place I completed the trip, about another 1500 miles, with the same condenser. I have never had vapor lock. I use the Marvels Mystery (MMO) oil, 2 oz. to a tank. I will increase that to 4 oz, per tank through the summer. ATF (automatic Transmission Fluid) will work well also. Doesn't have to be the F type which is Ford specific, since it is being sucked into the engine and not the tranny.
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Old 03-20-2015, 11:53 PM   #24
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Default Re: Fuel line shield to prevent vapor lock?

Thanks to all who posted such great pictures and comments!

I also have the original-style "waffle" exhaust manifold (and Autolite heater on top of it), and was kinda wondering if that might also produce more heat going down towards either the fuel lines or the carburetor?
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Old 03-20-2015, 11:54 PM   #25
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Default Re: Fuel line shield to prevent vapor lock?

Mike K
I agree, in So Oregon we have temps into the 100° area often and I've never had a problem nor do I know of any, and yes under conditions you describe. March is typically not that warm so me thinks something else is up.
I do use MM in my gas.
Note I have seen clothespins on gas lines but I'm touching that one. We did have a fellow complain during a parade in very mild temps that he was vapor locking. I said it's just not hot enough nor have you had enough time to "heat soak" the engine. He had a rusty tank btw...
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Old 03-21-2015, 12:07 AM   #26
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Default Re: Fuel line shield to prevent vapor lock?

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I made this heat shield when I was having vapor lock problems. Usually boiling in the carburetor is the problem. No problems since it was installed.


I had problems in warm weather idling, especially after a hard run. I did the deflector pretty much as shown, and it helped a lot. Shoot the carb on both sides and at both ends of the exhaust manifold, with a temp gun, and you will be amazed. The shield defintitly cooled the carb down.
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Old 03-21-2015, 12:59 AM   #27
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Default Re: Fuel line shield to prevent vapor lock?

Here's a picture of my gas line white cover. If you can't find white, you can paint a black one using white paint made for plastic.
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File Type: jpg Gas Line Cover.jpg (76.2 KB, 50 views)
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Old 03-21-2015, 06:53 AM   #28
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Default Re: Fuel line shield to prevent vapor lock?

I worked on old Datsuns for MANY years & they had a glass window in the carb. After turning off a hot engine, the gas would BOIL in the carb, after a few seconds!!
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Old 03-21-2015, 07:07 AM   #29
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Default Re: Fuel line shield to prevent vapor lock?

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Originally Posted by Tom Wesenberg View Post
I used some of that split plastic tubing that newer cars use as a wiring harness, except I found some white, which reflects the heat. It helped my fuel problems caused by crap gas. Once I found and bought the good gas I was able to remove the white plastic wrap. I also add 4 oz. MMO to each 10 gallons of good gas.
I do as Tom does and add about 4 oz of MMO to each tankful. There was once a vendor that promoted this at Hershey. I have been using it for 20 years with no problem. I did a parade last year when the temperature was high 90's and I was one of the few antique cars that did not experience vapor lock. Many blamed the problem on ethanol but vapor lock had been around a lot longer than ethanol. My Dad used to say that vapor lock was God's way of telling you to pull over and have a cool drink. When the drink is gone, so is the problem !
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Old 03-21-2015, 07:22 AM   #30
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Default Re: Fuel line shield to prevent vapor lock?

There is no such thing as vapor lock in a Model A. The carb gets hot and boils the gas out of the bowl. Next time it happens, just pour a bottle of water on the bowl. The heat shield that was mentioned shields the dist. from the manifold heat to save the condenser. It does nothing to protect the carb. Our club has this problem, but only during severe conditions, such as a hot parade or very slow driving. It usually happens right after you pull away from a gas station after a short stop. It has not been enough of a problem that we have done anything about it. If you are going to be in a very hot parade, try wrapping the carb with a wet rag, and keep it wet. jack

Last edited by Jacksonlll; 03-21-2015 at 01:27 PM.
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Old 03-21-2015, 08:54 AM   #31
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Default Re: Fuel line shield to prevent vapor lock?

I've had vapor lock when the temp is in the high 70's or 80's. It also happened to my friend when I was riding with him. He slowed down to make a turn and the engine quit due to lack of gas. It was boiling in the carb and line. He was able to restart it after a minute and finish driving the two blocks to his house.

After being parked at the Twin Cities Ford plant a few years ago on a hot day, my car only fired a few times and then no more. I had to unscrew the fuel line at the carb to get the gas to start flowing again. Two hours later I was at the New London to Brighton antique car run and the exact thing happened again. Since changing to good gas I've never had a fuel related problem.
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Old 03-21-2015, 09:09 AM   #32
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Default Re: Fuel line shield to prevent vapor lock?

Once talked to a guy that had a 'vapor lock' problem.

Went away when he tore down his engine for other reasons and found his valve clearances slightly off. Only on the hotest days the valves expanded just enough to cause the engine to stop running.

The Model A properly brought back to A specs will run fine.
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Old 03-21-2015, 09:54 AM   #33
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Default Re: Fuel line shield to prevent vapor lock?

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Originally Posted by Kevin in NJ View Post
Once talked to a guy that had a 'vapor lock' problem.

Went away when he tore down his engine for other reasons and found his valve clearances slightly off. Only on the hotest days the valves expanded just enough to cause the engine to stop running.

The Model A properly brought back to A specs will run fine.
Vapor lock was a problem from the time they were new. I have read several articles of people stopping beside the road and throwing water on The fuel system. Wayne
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Old 03-21-2015, 11:05 AM   #34
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Default Re: Fuel line shield to prevent vapor lock?

I only had this issue once in 60,000 miles of driving on completely
stock Model A after idling in line for an hour at the border crossing on a 97 degree day.

Perhaps, I've been fortunate with a good cooling system.
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Old 03-21-2015, 11:43 AM   #35
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Default Re: Fuel line shield to prevent vapor lock?

I've been either driver or passenger in Model A's for 57 years. Never once has there been a vapor lock problem. Never used anything except gas in the gas tank. Never used anything except a bare fuel line.

If your carb is starving of gas the problem is likely one of these:
1. Rust in the gas tank.
2. restrictive non - stock fuel filter.
3. Grose jet instead of a needle / seat in the carburetor.

Bone stock a Model A is extremely reliable. I drove a '30 Model A sedan to high school in 1974 - 75. Drove it from Minnesota to Texas in June of '75.
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Old 03-21-2015, 12:14 PM   #36
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Default Re: Fuel line shield to prevent vapor lock?

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Vapor lock was a problem from the time they were new.
And Wayne was there to witness it in person too!!

Sorry Wayne, had to go there...

Seriously, Just a couple of weeks ago my Town Sedan started acting up after a short stop, missin' and belchin'. Ran fine all other times. Had me scratching my head because if I babied it (running at low RPM and short shifting) it would sort itself out and run fine again.

I think the gas might be perking while stopped and running a low speed gives the incoming gas time to 'cool' things down.

I haven't had the chance to try some of the "remedies" suggested here (it's ~ 65°F right now) but I'll start with some MMO since I already have some (for lubing my butterfly).
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Old 03-21-2015, 01:11 PM   #37
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Default Re: Fuel line shield to prevent vapor lock?

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And Wayne was there to witness it in person too!!

Sorry Wayne, had to go there...

Seriously, Just a couple of weeks ago my Town Sedan started acting up after a short stop, missin' and belchin'. Ran fine all other times. Had me scratching my head because if I babied it (running at low RPM and short shifting) it would sort itself out and run fine again.

I think the gas might be perking while stopped and running a low speed gives the incoming gas time to 'cool' things down.

I haven't had the chance to try some of the "remedies" suggested here (it's ~ 65°F right now) but I'll start with some MMO since I already have some (for lubing my butterfly).
Dont apologize I found it funny. But I think. Have read every book ever produced about the Model A. Automotive engineers have even endorsed the procedure of dousing it with cold water to get rid of vapor lock.Wayne
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Old 03-21-2015, 01:47 PM   #38
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Default Re: Fuel line shield to prevent vapor lock?

I would love to hear a scientific explanation of how spearmint oil, light weight petroleum oil, and red dye helps anything when added to your gas in the amounts specified on the Marvel Mystery Oil can.
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Old 03-21-2015, 01:52 PM   #39
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I would love to hear a scientific explanation of how spearmint oil, light weight petroleum oil, and red dye helps anything when added to your gas in the amounts specified on the Marvel Mystery Oil can.
A good project for you. Write or email the company and ask your questions. Wayne
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Old 03-21-2015, 02:03 PM   #40
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Default Re: Fuel line shield to prevent vapor lock?

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I would love to hear a scientific explanation...
Reminds me of when I worked in the oil refinery (Worked for Chevron USA for 25 years). Every so often a 'new' engineer would come up with some "NEW" way to cut costs, make more or eliminate a job and we, the people that actually boiled the oil (ran the refinery and blended the product to spec) would say it won't work.

Engineers: It show it works on paper
Refinery Operators: "Won't work" or "tried it before"
Managers: Engineers are the educated ones, we'll do it.
Results: Spent lotsa Money, didn't work, eliminated new procedure and S/D new equipment.
Moral of the story: Sometimes you gotta go with something that works even though there isn't a "scientific explanation".

Last edited by Y-Blockhead; 03-21-2015 at 04:00 PM.
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