Vapor lock

[carolinamudwalker]

What exactly causes vapor lock? And how can changing to another up-draft carb be a cure? Is it the engine itself running to hot in the summer? Or is it the carb sucking in hot air from the exhaust manifold? I have read the service bulletins cover to cover and there is no mention of there being a problem back in the day so what gives? Bob

[BRENT in 10-uh-C]

Ohh, I'm so grabbing a bag of popcorn while I sit back and watch this one unfold!!

Bob, this has been debated several times in the past here. Folks say that it is because of cheap fuel & the underhood temps however they cannot explain why the same phenomenon does not happen to all of the riding mowers out there! My personal opinion is folks will only believe what seems believable to themselves!!

[harleytoprock]

I've always heard the term " vapor lock" but have never experienced it. So what is it?

[Mitch//pa]

Good post Brent to get things going

[Kevin in NJ]

Vapor lock- What to call a problem when you do not know the solution.

The true vapor lock is a condition on cars with pumps where too big a bubble appears in a fuel line and the volume of each push of the fuel pump can not push through the bubble. We had this problem in our 39 Ford. The fuel pump was marginal and the heat of a parade would get to it. We knew the problem because there was no gas in the carb. A rebuilt fuel pump fixed the problem.

For example, One person told me about how he believed in vapor lock cause his car kept stopping when it was hot out. He tried everything to fix vapor lock and it did not get fixed.
The engine had to come apart for other reasons and he found some of the valves were marginal with their clearances.
He put the engine back together properly and the engine no longer would stop for no reason. It just kept running.

More often the problem is electrical. A borderline coil, a flaky wire, or a condenser that is not happy.

You have to imagine what might happen. A few valves with the gap set wrong, a worn cam that has some variation of the lobes, a block with some rust scale, a carb not set right and so on. Each engine is going to have a point which takes it over a line.

So the problem can be subtle and the result of several things each seeming to be in spec. Under the right conditions they rear their ugly head.

The thing to understand is the engine does not normally have a problem. If you have vapor lock do not buy into the standard treatments. The problem is you may have to dig very deep to find the issue.

[BILL WILLIAMSON]

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I feel that it's mainly caused by gas BOILING in a HOT carburator, after shut down.
Bill W.

[Gold Digger]

There's definitely a problem when you unscrew the gas line at the carb and only gas steam come through for the first few seconds.

[marc hildebrant]

It is a real problem that can happen on hot days.

Sadly, the so called experts on the forum do not trust that people can have this problem because "they" say it can't happen.

I have had vapor lock occur on hot (100 degrees) days in Colorado after a good high speed run down the "diagonal" (Longmont to Boulder road).

After stopping at a traffic light, my Model A ran rough and I needed to pull out the choke to keep it running. After a brief trip after the light, the car ran fine. Only happened with straight 10 % ethanol gas and only when the temp was around 100.

Marc

[Tom Wesenberg]

Exactly what Marc said, except I've had it happen on 80* days when using the crap gas. I've never had a problem as long as I use the good gas without corn crap in it.

I've also experienced what Gold Digger said, and it happened twice in one afternoon when the temp was about 80* and I was parked for a couple hours. The engine wouldn't start because the crap gas had boiled away in the carb, and I couldn't restore flow until I disconnected the fuel line at the carb. As soon as the crapahol started flowing I reconnected the line and drove home.

My 1952 Studebaker Land Cruiser has the fuel pump mounted up high on the V8 engine, and this should really lead to vapor lock, but that car never gave a problem because we had better (real) gas in the 60's and 70's. This is the main reason for putting the electric fuel pumps inside the gas tank these days. It keeps the entire fuel line under pressure, so you don't have vapor forming in the line.

[captndan]

Originally Posted by marc hildebrant

It is a real problem that can happen on hot days.

Sadly, the so called experts on the forum do not trust that people can have this problem because "they" say it can't happen.

I have had vapor lock occur on hot (100 degrees) days in Colorado after a good high speed run down the "diagonal" (Longmont to Boulder road).

After stopping at a traffic light, my Model A ran rough and I needed to pull out the choke to keep it running. After a brief trip after the light, the car ran fine. Only happened with straight 10 % ethanol gas and only when the temp was around 100.

Marc

More on that. And yeh I knew the diagonal since it was a toll road. Vapor lock was common back in the 40's and 50's. It was no ethanol then and altitude had something to do with it. So, if your car had the problem in the summer and at high altitude you wrapped the gas line loosely with tin foil and held it on with clothed pins. Remember the canvas water bag? Cool water was poured on the fuel lines and the carburetor. I don't know the science but it did work.

[JohnLaVoy]

I will be running a complete description of the cause and what to do about it in the Times in the Summer issue. Basically it is the boiling (vaporizing) of the fuel before the carburetor.

[C26Pinelake]

Two of the experts have spoken ( Brent and Tom ) with opposite opinions! So no matter what, this subject will never reach a conclusive answer! Wayne

[jimalabam]

Ur OH! Get the wooden clothes pins out of storage. hee hee...

[Steve Plucker]

Great question but I hate to say this guys...but in all my 35 plus years driving Model A Fords (winter, summer, spring or fall)...I have never experienced "Vapor Lock". Hmmmmm...Better "Knock On Wood" with that one.

So tell us Mr. One Star...why is this not an important question to you?

Interesting.

Pluck

[Steve Plucker]

Originally Posted by JohnLaVoy

I will be running a complete description of the cause and what to do about it in the Times in the Summer issue. Basically it is the boiling (vaporizing) of the fuel before the carburetor.

We will be waiting for this one!

Thanks John.

Pluck

[richsfords]

When the "vapors" hit we would use the cloths pins and/or would wrap HD aluminum foil around the fuel lines.
On the way to delivery our clubs toys to the Salvation Army this Christmas it happened to my A. plus overheating for the first time. I never use the corn EPA fuel.

Richard in New Bern

[mshmodela]

In my newbie opinion if corn base fuel sits in a hot carburetor (after a drive) the fuel may turn to vapor more easier than 100 gasoline. I think though with cool fuel from the cowl tank flowing in the the bowl that's not likely to happen... But once you turn the car off and let it sit... you might in theory experience this... Tests and experiments could likely proves this once and for all... I might take a carburetor with a small port-hole on the side of the bowl and a camera to really prove or disprove...

[JohnLaVoy]

A short version, altitude, temperature and fuel make up all create the problem. The last trip over the Continental divide on the 2012 Summer Tour 24 of the 25 Model As suffered the vapor lock condition.

[BRENT in 10-uh-C]

Originally Posted by JohnLaVoy

A short version, altitude, temperature and fuel make up all create the problem. The last trip over the Continental divide on the 2012 Summer Tour 24 of the 25 Model As suffered the vapor lock condition.

But is the root problem because of the fuel, ....or a mechanical issue that is the cause? (i.e.: "My Model-A always runs hot ...but I don't use a cooling fan." or "Model-A lights are too dim on 6 volts so I replaced my dingy original reflectors with sealed beams.")

[Big hammer]

Apple slices go good with popcorn Brent! AER in his instructions on operating his engines
says to not close GAV past 1/2 open, because of the nitrogen enriched fuels today!
This extra flow would help with vapor lock? Is the nitrogen enriched fuel the same as
corn gas or is it a double wamy?

[Y-Blockhead]

Originally Posted by mshmodela

In my newbie opinion if corn base fuel sits in a hot carburetor (after a drive) the fuel may turn to vapor more easier than 100 gasoline. I think though with cool fuel from the cowl tank flowing in the the bowl that's not likely to happen... But once you turn the car off and let it sit... you might in theory experience this... Tests and experiments could likely proves this once and for all... I might take a carburetor with a small port-hole on the side of the bowl and a camera to really prove or disprove...

When I was new to my Model A I would shut off the fuel while I went into a store (or where ever) and when I went to restart it would back fire and run terrible until I let it set awhile.

When I started NOT shutting off the fuel it did not act up. I can only assume that with the fuel shut off the gas in the carb got hot. Leaving the fuel turned on may have had a cooling affect.

I can think of no other reason for this phenomenon.

So now I just leave the fuel turned on all the time except when parked overnight.

Originally Posted by Big hammer

because of the nitrogen enriched fuels today!

I have never heard of "nitrogen enriched fuels". What would be the purpose of that. N2 doesn't burn and is lighter than air so it would just evaporate.

[Jerry in Shasta]

It happened to us on a long tour. We pulled a long 6 mile gentle climb, temperature 100+, elevation 2000'. Mostly high gear but some second.

About 5 miles in to it, she shut down. Slapped some ice on the carb. and we up and going in 10 minutes we were up and going.

Made the rest of the climb with the hood halves propped open, and in second gear.

[Big hammer]

She'll oil at their pumps has some wording of nitrogen enriched fuel
I thought nitrogen as a gas, and would dissipate and had a good laugh!
I just pump it then go drive :-)

[TerryH]

I've asked this before, but never got an answer or even a comment: why is that many of us who live in California, and can buy only "crap gas" with corn in it, drive on hot summer days, and never experience vapor lock? If the gas were the main problem, then we would see far more cases of vapor lock in all those states that do not have fuel choices.....thoughts????? And I don't like crap gas....My main problem with it is my mileage surely suffers some....

[BRENT in 10-uh-C]

Originally Posted by TerryH

I've asked this before, but never got an answer or even a comment: why is that many of us who live in California, and can buy only "crap gas" with corn in it, drive on hot summer days, and never experience vapor lock? If the gas were the main problem, then we would see far more cases of vapor lock in all those states that do not have fuel choices.....thoughts????? And I don't like crap gas....My main problem with it is my mileage surely suffers some....

I'll give you my opinion, ....there are WAY more folks out there who drive their Model-As on tours (-with the same gasoline) with frequency that never experience any type of "vapor lock" issue. Therefore how can they write about vapor lock?

Now the one thing I have noticed many times is that modern fuels go stale within a short period of time. Even 60 day old fuel will create driveability issues. Is it vapor lock? No, but folks gotta blame it on something. Ironically, how poor do we think the fuels were back in the depression era? Did the Model-A run on it then??

[carolinamudwalker]

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Well, I feel better (I think) knowing it is not just me. Looking forward to summer Model A Times. Bob New Bern N.C.

[George Miller]

You will never have a problem if you leave the car in the garage.

[Steve Plucker]

Originally Posted by George Miller

You will never have a problem if you leave the car in the garage.

Now George...That is no way to treat a Model A!

Pluck

[Tom Wesenberg]

Originally Posted by forever4

Why does this thread start with post # 2?
What happened to post # 1?

I see all the numbers OK on this thread, but for the past few months my computer has had a problem with the numbers on many posts. It might show 20 posts, but lists a page 2, which isn't right because page 2 should have post #21. If I click on page 2 it just takes me back to the top of page one with post #1.

I thought it was just my computer that was vapor locked.

[700rpm]

Originally Posted by BRENT in 10-uh-C

I'll give you my opinion, ....there are WAY more folks out there who drive their Model-As on tours (-with the same gasoline) with frequency that never experience any type of "vapor lock" issue. Therefore how can they write about vapor lock?

Now the one thing I have noticed many times is that modern fuels go stale within a short period of time. Even 60 day old fuel will create driveability issues. Is it vapor lock? No, but folks gotta blame it on something. Ironically, how poor do we think the fuels were back in the depression era? Did the Model-A run on it then??

As usual, Brent has got it right. I just poured off 5 gallons of corn gas that had sat in my sedan for two months. The car, which normally performs beautifully, would barely start, then not run at all. I felt like I'd whipped a puppy. I put two gallons of real gas in and we're back to normal.

In 55 years of driving a Model A in all kinds of conditions I have never experienced anything like vapor lock. There have been high altitude effects, and loose wires, and overheating, but nothing I would call vapor lock. Just one man's experiences.

[ed thibodeau]

I leave 10% gas in my vehicles all winter and have never had a problem starting or running. In my 8N it sometimes sets for a year and again it has no problem starting or running.

[700rpm]

Originally Posted by ed thibodeau

I leave 10% gas in my vehicles all winter and have never had a problem starting or running. In my 8N it sometimes sets for a year and again it has no problem starting or running.

Oregon is notorious for high priced poor quality gas. Plus, we had something like 120% humidity and record rainfall from Nov. 1 - Dec. 31.

[30aadoodlebug]

There was a great article in Hemming's Classic Car about a year ago. When I find it, I'll post. Have fun with the popcorn...

[marc hildebrant]

With regard to the "vapor lock never happened to me, so it can't be true..."

My Model A has always started, so anyone that hasn't been able to start their car must not have a problem...eh?

Marc

[mshmodela]

[QUOTE=Y-Blockhead;1216674]When I was new to my Model A I would shut off the fuel while I went into a store (or where ever) and when I went to restart it would back fire and run terrible until I let it set awhile.

When I started NOT shutting off the fuel it did not act up. I can only assume that with the fuel shut off the gas in the carb got hot. Leaving the fuel turned on may have had a cooling affect.

I can think of no other reason for this phenomenon.

So now I just leave the fuel turned on all the time except when parked overnight.


Makes sense... In fact it might be actually safer... I happen to have flown on TWA 800/803 in 1995 about a year before that accident and that was a hot fuel vapor explosion... Keeping fuel in liquid form as opposed to vapor is saver during storage...

[Dodge]

I used to have a vapor lock problem with my 49 Ford V-8. It has the fuel pump on top
of the motor and on a hot day pulling a steep long grade it would act up. I got to carrying
a cooler with ice in it. I would get out and dump ice on the fuel pump and she would start
right up again and run the rest of the way up the grade. I think it was vapor lock.
I had another problem with the crap gas here in California a few years back when they
must have changed the gas forumla. I have a 1915 Model T which is hand cranked.
I have been cranking this car for 50yrs. so very familar with it.
I had filled the tank and parked the car. A week later I took the car out for a drive. It
started just like always when it was cold in the garage. One pull with the choke on and
one or two cranks and started right up. I went to the hardware store about a 10min. drive and went in a did some shopping. I was gone about 15-20 mins. and came out
to start the car. Usually it starts on one crank with no choke under this condition but
this time I cranked and cranked. I choked it a couple of times and nothing. I thought maybe I had flooded it so I pulled a plug, it was dry as a bone.
I went to the burger joint next door and got a cup of ice, threw it on the manifold and
it started right up. This happened a couple of more times after this so I called the tech
line for Arco gas. The tech told me they had indeed changed the formula and some older
cars had to crank a little longer as the fuel was evaperating in the hot intake manifold
before it could get to the cylinders. When I explained that I was the cranker and how
dagerous it would be I it happened in the middle of an intersection, he suggested I
put the mid range gas in it as it wouldn't evaperate as quickly as the cheap gas.
I did this and haven't had a problem since.

[CWPASADENA]

The Flathead V-8's are especially bad about vapor lock with todays "Corn Gas". We have found adding a little Diesel fuel in the gas usually solves the problem. Real gasoline from the "old days" had a higher vapor pressure than todays blended fuels. Add about a pint for every 10 Gals of gasoline. The diesel will raise the vapor pressure or boiling point of the gasoline.

I know there are some who will say that this is not good for your engine as the Diesel will also lower the octane of the gasoline but we do not have a high enough compression ratio to have a detonation problem.

The Diesel will also add a little lubricant to the fuel which is good for the engine. This amount of Diesel will not fowl the plugs or cause a model A engine to not run right.

My experience and my experience.

Chris W.

[Mike V. Florida]

Originally Posted by Y-Blockhead

I have never heard of "nitrogen enriched fuels".

Shell Nitrogen Enriched Gasoline

[Mike V. Florida]

Originally Posted by marc hildebrant

With regard to the "vapor lock never happened to me, so it can't be true..."

My Model A has always started, so anyone that hasn't been able to start their car must not have a problem...eh?

Marc

I absolutely believe something is happening, vapor lock, or something else. Too many owners are having a problem.

Here in florida we have, hot days, cool days, high humidity, low humidity, and even "corn" fuel. My club does not seem to have any problems. There is nothing worse that a problem with no solution, especially when you read that others with the same car do not have the same problem.

I think Brent has come the closest, the problem is not a Model A problem but rather an individual setup problem. Timing, timing while driving, GAV setting, engine wear, electrical grounds, air flow, and so on and so on all make a car an individual. Some individuals have common traits.

[MikeK]

Just reading this thread has given me the vapours! Living in Chicago I see what is called seasonal fuel formulation changes, or what is called winter and summer blend. Mid January the fuel has so much butane content it will boil in your hand. OK for quick sub-zero starts and no problem in injected vehicles with vapor recovery and high pressure fuel feed. Trash in carbureted anything. The 'summer blend' has a much higher vaporization point. Despite both being E10 the summer blend stuff is OK @ 100F, the winter blend stuff makes the A suffer when it hits 75F+.

My Honda lawn mower won't run on the winter blend stuff after the engine gets hot. You can take the gas cap off and watch the boiling vapor bubbles backing up from the hot carb and condensing (disappearing) into the cooler liquid fuel. Not an alcohol problem, a butane problem. Unlike propane, butane is a cat refining product with little commercial market. They try to dump as much as possible into gasoline. What is accumulated from refining during the summer, unfit for that blend, goes into the winter blend. Refining blends vary by region, refinery, and season.

Henry's 1920's - 30's gas had a significantly different vapor pressure, as did the fuel all through the carburetor era. Not too good for 0F starting, though. I'd love to join in and put the blame on ethanol, but that's not the heart of the problem. Evolving and changing fuel blends and vapor pressure specs to suit modern vehicles are the real problem IMHO.

[Bob Johnson]

I have had a problem several time with my Model A. I would not call it vapor lock. It happens when I slow down or more often when I stop right after a long run at speeds over 50 mph on a hot day. Here in California we have winter and summer gas. It happened once in December when we had a very hot week, over 80 degrees. I think it was because the winter gas boils out of the carburetor easier than the summer gas. When it happens all I have to do is open up the GAV and everything is fine. Depending on how bad it is I have to open the GAV 1 to 3 turns. After a couple of minutes I can turn down the GAV. One time I was going up a long steep grade. I have to open up the GAV 1 to 1.5 turns to keep the engine running right. Once I got over the hill I stopped for gas and the carburetor was so hot a drop of water would instantly sizzle and boil off of it. I used a gallon of water to cool down the carburetor. My analysis is that the carburetor gets hot enough to boil the gas. This is most likely to happen when you pull off of the highway and come to a stop. The residual heat in the engine super heats the carburetor. Since the gas has vaporized in the carburetor not enough can get through the main jet and the mixture is too lean. By opening up the GAV there is a second jet supplying gas and the mixture is corrected. Once the carburetor has cooled the gas is no longer boiling and the GAV can be turn down.

I do not have engine splash pans. Perhaps they might help the air flow to the carburetor and prevent the boiling gas.

Bob

[MikeK]

Painting the carb gloss appliance white to reflect the heat rather than the black that absorbs heat may help, but the purists with alternators and 16's would point fingers and have a stroke.

Putting a sheet metal heat reflector around the carb may help too, but the purists with heater holes chopped in their firewalls and aftermarket dizzy heat shields would point fingers and gasp.

Alcohol will help too, but only if you put it in a glass and drink it. By the time you're OK to drive again the engine will be stone cold and run just fine. The purists will wave bibles at you and lament the repeal of the 18th and the Volstead act.

[carolinamudwalker]

Ok, re-reading all the post's, heat seems to be a common thread. And the reason this was not a problem in the 30's is because of the fuel blends have changed! (Mike post #40) We hear adding all sorts of concoctions to the fuel: Diesel, ATF, Marvel mystery oil ect. is the cure. But I like Brent's post #2 " Folks will only believe what seems believable to themselves." going with that I like Bob Johnson's post #41 because it is just like the experience I had but was not smart enough to figure out the solution to get home. I know that I am going to hell for this but if it happens to me again that updraft carb. is history. Ill wait for John's report in the model A times before taking the drastic step of tossing the Zenith. Forgot one other post, "each car is different in the way it has worn, how it is tuned, and how it is driven." This may explain why some drivers have never experienced this problem. Sorry don't remember the post. Bob New Bern N.C.

[George Miller]

Originally Posted by carolinamudwalker

Ok, re-reading all the post's, heat seems to be a common thread. And the reason this was not a problem in the 30's is because of the fuel blends have changed! (Mike post #40) We hear adding all sorts of concoctions to the fuel: Diesel, ATF, Marvel mystery oil ect. is the cure. But I like Brent's post #2 " Folks will only believe what seems believable to themselves." going with that I like Bob Johnson's post #41 because it is just like the experience I had but was not smart enough to figure out the solution to get home. I know that I am going to hell for this but if it happens to me again that updraft carb. is history. Ill wait for John's report in the model A times before taking the drastic step of tossing the Zenith. Forgot one other post, "each car is different in the way it has worn, how it is tuned, and how it is driven." This may explain why some drivers have never experienced this problem. Sorry don't remember the post. Bob New Bern N.C.

Plus a lot of them do not have our gas blends and live in the heat of NC in the summer.

[Tom Wesenberg]

I'm glad Mike posted about the fuel formulation because I've said for years that even when I buy the good gas without corn crap, it still isn't the good gas we had in the 60's and 70's, even if the lead is removed. Today's gas quickly evaporates, and much faster than it did years ago. It also hurts my hands, which I think is the corn crap mixture. Notice how much the plastic gas containers puff up in the heat of summer. They never used to do that.

Before changing out the carb I would add a heat shield like a couple guy have done in the past. I have some white plastic wire wrap with the split seam, and just putting that on the fuel line helps.

In the 80's many cars were made with fans that blew outside air onto the carb or fuel pump for 3 to 5 minutes after turning the engine off. This was to keep the gas from boiling, so we know that the reformulated gas does boil much easier than it did in the good old days of good gas.

[woodypecker]

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People who have posted about problems were at altitude after pulling long grades. Even water boils at a lower temperature at high altitude. Ask any cook who has tried to cook in the mountains.

[captndan]

We can science this problem all we want but it comes down to basics. It takes high altitude, more than the car is used to, high ambient temp, low humidity, and fuel with a low vapor point. Add that old cars were designed for low altitude running. No need to design a fuel system that kept gas lines and pumps away from things like the exhaust manifold. So, if you and your car fall into these vapor lock areas do like the old timers did. Tin foil, cloths pins, copper wire, and cool water or ice. Happy Motoring!

[Mitch//pa]

Here it is in a nut shell
https://en.m.wikipedia.org/wiki/Vapor_lock

[steve s]

I think the Wikipedia link that Mitch gave pretty much settles it.

A few details that some earlier posts had confused:

A liquid's vapor pressure and its boiling point vary in opposite directions. A liquid will boil when its vapor pressure matches atmospheric pressure. So, liquids with lower vapor pressures will have to be heated to higher temperature before they will boil.

Ethanol and gasoline form a highly non-ideal solution: neither the vapor pressure nor boiling point of mixtures can be predicted by simple interpolation between the values for the two pure liquids. In fact, adding small amounts of ethanol makes the lighter fractions (e.g., butane) want to evaporate even more readily, thereby lowering the initial boiling point. This fact was a major technological hurdle that the oil companies had to solve before gasohol could be sold. There was an air pollution tradeoff: ethanol gave a cleaner burn and exhaust, but the increased hydrocarbon load put into the atmosphere (due to evaporation during fueling up, etc.) created more smog.

[BILL WILLIAMSON]

I "wonder" if starting problems, after a few months' storage, "might" be caused by a BIG BELCH of WATER, accumulating in the carb bowl? This is common in small engines.
This could be overcome by pulling the carb drain plug & turn the gas on, until good gas appears.
Bill W.

[Synchro909]

We had a chemist from a fuel company give a talk at a club meeting a while ago on this topic. In brief, what he said was that fuel is a mixture of many different hydrocarbons, each with a different boiling temperature. Vapour lock happens when the fuel or at least part of it boils, producing a vapour. No surprise there! In the old days, enough fuel to meet the demand was able to be produced using a narrow range of HC's with similar boiling temps. They were selected to give satisfactory performance in normal driving conditions. As the number of cars on the road increased and demand followed, refiners had to widen the range of HC's they put in the fuel to keep up with it. Some had higher boiling temps, others, had lower ones. This pattern has continued for many years now and the range of boiling temps is very wide, some of them boiling at very low temperatures. It is these low boiling point HC's that cause the problem.
If you leave modern fuel to evaporate, you will notice that there is a dark coloured fluid left behind that looks like a light oil. Surprise, surprise - that's exactly what is. Oil is only another HC but with a higher boiling temp.
If you now reread the above posts, I'm sure most will now make sense.

[carolinamudwalker]

Well there you go people, Mitch post # 40 has the answer, we just need to all use Aviation fuel. In all seriousness Mitch"s link is very informative. If you want to keep your Zenith carb, why stop at custom heat shields and tin foil draped over the fuel lines? How about a heat exchanger tube over the fuel line,pump water thru it to a small radiator mounted on the front bumper? Of course we will need a 12v pump and fan. Or we can accept that the EPA is hell bent on making the fuel even worse in the near future and bite the bullet and install a modern downdraft carb and be done with it. I am only talking about long range touring hear not your show cars or those that stay within 100 miles from home. Ok I am going back to my closet. Bob

[G.M.]

I live in SW Florida and it's 85 plus a good part of the years. I had many
vapor lock problems with corn gas. On 100 degree days I had vapor lock
on 3 or 400 mile turn pike runs. At 65 or 70 MPH it ran good but if there
was road construction or an accident below 55 MPH VL started. Getting
back up to speed it went away. Also local driving, stopping for lunch for
1/2 the heat build up would cause VL. I did tests for several months under
the same conditions and determined after numerous "fixes" if the pump
was kept cool (fans and heat sinks) the problem went away. The problem
on the interstate proved that as long as a GOOD flow of cooler fuel from
the tank flowed through the pump it cooled it enough to prevent VL. I
installed a small fuel return line with a 'T" in the line right after the fuel
pump back into the filler pipe of the tank. There needs to be enough fuel
flow to the carb for high speed driving so you can't return to much. The
Stromberg carb has a fuel restriction hole in the float valve. It was
determined by Ford a .098 hole was ideal. A few thousandths larger
allowed fuel to push by the valve and a few thousandth less starved the
engine at high speed. This is described in the Ford Service Bulletins.
I found a restriction hole of about .100 allowed enough fuel return to cool
the pump and supplied enough fuel for at least speeds of 85 MPH. I don't
like electric pumps so this is my method. I also now run noncorn gas
because the alcohol attracts water, rusts the fuel tanks and eats the thin
brass float. This won't work on "A"s but defines the problem. G.M.

[BILL WILLIAMSON]

Some of our guys have run out of gas, with a warm engine, & the added gas WOULDN'T fill the carb. "Apparently" due to "back pressure" in the HOT fuel lines, carb, & sediment bowls. Just pour COLD water on all that stuff & IT RUNS AGAIN.
Bill W.

[mshmodela]

Boiling gas in a carburetor float bowl:

https://www.youtube.com/watch?v=yfm6DrB0eV8

[Chuck Sea/Tac]

Dodge, where are you located? Heat related: guessing your Southern Hemisphere .