Vapor Lock

tdlmomowers

tdlmomowers

Senior Member
Looking for some advice on what other Ford Barn readers have done to cure vapor lock on Model A Fords. My son-in law has a 29 coupe and yesterday he had an issue with vapor lock after shutting his car off after a long ride. Has anyone had any luck with using a 4 blade fan or insulating their fuel line. Any other ideas would be appreciated.
 
you dont get vapor lock on gravity feed carbs, the fuel runs down hill no matter what, if it hard to start after a long run the fuel is probably being evaporated or boiled in the carb causing a rich starting problem, they make a heat shield that goes between the carb and manifold mount, it deflects heat away from the carb, check all the fuel delivery system, make sure none are restricted, might even be an electrical problem
 
Yep, here we go again with the vapor lock mystery. Everybody has a cure for a problem that I believe is misdiagnosed. Like ford1 said, "you don't get vapor lock on gravity feed carbs, the fuel runs downhill no matter what". Something is blocking the fuel flow. With an eighty year old gas tank, there is likely to be rust scale or trash of some type in the fuel system. That trash can move around and cause a blockage and then get sloshed around to mysteriously allow free flowl. That unexplainable interruption of fuel flow triggers people to call it vapor lock.

Cleaning the gas tank is a whole new thread that has been posted many times.
 
http://www.fordbarn.com/forum/showthread.php?t=3803&highlight=vapor+lock+nonbelievers

HEre's a link to an earlier thread in which I gave my complete brain dump on the phenomenon.

It's a contentious issue that reminds me of PMS: those who have not personally experienced it are convinced those who have are faking it. Also, there's a bit of a semantic quibble over the distinction between "lock" and really really crappy running.

I got some relief from insulating the sediment bowl and fuel line and installing a home-made heat shield between carb and motor/exhaust manifold. However, for me, the final solution seems to be using the newer replacement Zenith carb (#13922), which is a whole other topic of derision. If you can avoid ethanol, it will help. Others claim various additives help; none worked for me.

Steve
 
An exhaust manifold leak can cause a hotter than hades condition of the manifold. Rule that source of heat out before other modifications. At what temperature do you suppose the fuel you use has to be to boil?
 
I would be willing to bet that the crappy gas we get now probably boils at 150 degrees or even less if it's wintertime formulation. The thing you need to understand is that your modern car uses a pump back in the cool tank pushing fuel up to the fuel injection system and doesn't care what temperature the gas boils at. Oil companies and the EPA couldn't care less that there are still carbureted cars out there and are, in fact, doing everything they can to make sure you can't use one anymore.
 
I have heard guys complain about "vapor Lock" and others say that a gravity feed system cannot vapor lock. In any case here is what does happen in my car. In hot wx and after a full temperature warm up drive and then I stop for a time for a snack or such, I can restart the car and get about a block down the road and it will quit. I have discovered that I can loosen the 5/8 head plug on the front of the top casting of the carb and I get a hissing of escaping vapor. Let it escape and retighten and I am off again. What happens is the fuel in the float chamber or above it boils when sitting with no fuel flow while stopped. This boiling fuel forces fuel an "air" or vapor gap in the fuel supply. It releases when the plug is loosened and then when restarted ,which it will immediately, the fresh cool fuel prevents the carb fuel to overheat. This used to haunt me on tours in hot weather. I used to have to wait maybe 20 min. to get it to start again. Now It is so easy to fix that it is no problem to me.
 
I don't know what it is that makes my "A" balk and backfire then stop. It cools off and we're off and running. A little water over the fuel and carb. help the problem.

I moved the fuel line as close as possible to the side of the hood to get as much air flow as possible. Since then there has not been a problem
JB
 
Jerry in Shasta said:
I don't know what it is that makes my "A" balk and backfire then stop. It cools off and we're off and running. A little water over the fuel and carb. help the problem.

I moved the fuel line as close as possible to the side of the hood to get as much air flow as possible. Since then there has not been a problem
JB
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Jerry,
Sometimes coils overheat and stop working. The next time it dies on you, quick check and see if you have spark. If you do, consider some of the vapor lock ideas in the link I gave above.

Steve
 
There is a clothes-pin cure that absolutely works!
Do NOT try clipping them on the fuel line, that never worked for me.
Here is what you do:
Get a nice big sack of clothes-pins, all wood or spring type, your choice.
gu5A8LIhAqb5Fp-uEDxRYnYagl6SQU_1p-hXqTc_6ayIWA&t=1.jpg

When the car vapor locks, go and do your laundry. String a line and, using the clothespins, hang your laundry out to dry. It helps if you have some notched bamboo poles to prop up the line. After all is dry, folded, and the poles (optional), line and pins are put away, go start the car. Works every time.
 
My gravity feed Model A gets vapor lock when the air temp is up around 100 degree's.

The problem would occur when I stopped for gas or traffic light in the heat.
For me, it had to be around 100 , but, living in Colorado's front range, it got up to 100 often during the summer.

My solution was to move to a cooler climate !

Marc
 
Using ONLY gas with NO ethanol solved the problem for me.

If I use gas with 10% corn crap in it the car will balk and jerk when taking off from a short stop at the light or stop sign, if the temp is 80* or more. Pulling the choke part way would help some and by the end of 3 blocks the fuel had cooled enough for the car to run OK again. I haven't had one problem after changing to GOOD gas. Twice when I had the crap gas in the car and was parked for an hour or more, the car was vapor locked and gas wouldn't flow to the carb until I loosened the fuel line at the carb. As soon as I removed the line the gas would flow again and I could tighten the line and start right up. My gas tank, carb and fuel line are spotless clean.
 
ford1 said:
you dont get vapor lock on gravity feed carbs, the fuel runs down hill no matter what, if it hard to start after a long run the fuel is probably being evaporated or boiled in the carb causing a rich starting problem, they make a heat shield that goes between the carb and manifold mount, it deflects heat away from the carb, check all the fuel delivery system, make sure none are restricted, might even be an electrical problem
Click to expand...

Strictly speaking, you are correct. Vapor lock happens when you have a fuel pump and the fuel it is trying to pump has boiled (turned to a vapor). Each stroke of the fuel pump moves only a tiny bit of vapor, or nothing at all (because the pump was designed to pump a liquid, not a gas). With no fuel pump on a Model A, you can not have vapor lock in the traditional sense.

But the Model A is having problem with the delivery of fuel in hot weather, with high under-hood temperatures. We don't have to call it "vapor lock" (because that is reserved for situations with a fuel pump). Let's call it "vapor block". When the fuel in the carb and/or fuel line boils, it interferes with the proper operation of the gravity feed fuel system.

I suspect that the idle jet system keeps the car running at idle, even with the fuel level in the bowl getting low (fuel boiling off, not getting replenished), and then when you step on the gas to go, the fuel level is too low for the main jets to deliver what you need and you stall or run rough. That is why working the choke a bit to richen it up seems to get you moving again. (Normally, choking a hot engine is the last thing you would think of; too easy to flood it.)

I don't know why the fuel does not want to flow down under gravity to replace the boil off. Maybe vapor at the float valve is blocking the liquid fuel from coming through. Maybe it is a plug of vapor in the steel fuel line running down to the carb. That's why I call it "vapor block". A fuel pump might help push it through.

It is real. It happened to the guy I was riding with last month on a tour when going slow. You could tell it was fuel starvation from the way it died. He opened the hood, let things cool off a bit, poured some water on the carb and it fired right back up.

It happened to lots of folks in Dallas at the joint meet a few summers ago, sitting in the heat at the Texas Motor Speedway. After idling for a while in line, they got the signal to go out to the track and their engine stalled upon take-off. I'm pretty sure everyone got going after they opened the hood and cooled off.

We have no option to buy gas here without ethanol in it. That would be nice, but able to. I think it is an air pollution thing.
 
Despite the debate over the name of the issue the sure solution is fuel pressure. An electric fuel pump (a regulator may be necessary) is my solution of choice. I have one installed in one car and when the problem occurs I turn on the pump. Amazing the number of supposed electrical problems that fuel pressure solves almost instantly. In an emergency a container of ice cooling the sediment bowl is also effective. A foam drink holder wired on works well. I have A's that do and A's that do not have the problem for reasons I cannot explain.
 
steve s said:
Hotrodster said:
I would be willing to bet that the crappy gas we get now probably boils at 150 degrees or even less if it's wintertime formulation. ...QUOTE]

It's worse than you think; modern gasoline begins to boil at around 100 degrees F.

Steve
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Ethanol has a boiling point of 173.3 ºF therefor how can a mixture of Ethanol and Gasoline have a boiling point any lower than 173.3 ºF?
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MrTube said:
steve s said:
Ethanol has a boiling point of 173.3 ºF therefor how can a mixture of Ethanol and Gasoline have a boiling point any lower than 173.3 ºF?
Click to expand...

It's called non-ideal mixing of the positive-deviation from Raoult's Law kind. Molecules that may be perfectly happy to coexist closely in a liquid when surrounded only by their own kind can sometimes be rather desperate to escape the mixture when forced together with molecules of a different kind--not all that different from people!

But, even gasoline without ethanol boils below 173 because it is a mixture of varying molecular weights, some of which--like butane--are exceedingly volatile. Those are the ones that leave town first, with or without ethanol around.

Steve
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We were on tour late last summer during a hot spell. In general, those that filled up with 10% ethanol gas had problems while those that filled with premium non-ethanol kept on cruising. The problem cars were balking, backfiring, hard starting and losing power. There was one gent that used 10% ethanol gas but added a few ounces of two cycle oil to his gas. He had no problem...we added some Marvel Mystery oil to a couple cars that were having problems and the issues went away. A question for those that understand the chemical result of adding this product to the ethanol gas: Did the addition of the oil to the gas solve the problem or was it just chance that they improved?
Thanks for any comments!
Good Day!
Dave in MN
 
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