Vapor Lock 101 ?

steve s,

I also just got finished reading the thread that you posted. I am one of those guys in the hot weather South who has never had a problem. I wish the guy with the two Model A's that has the problem and the one without the problem would try switching carbs between the cars, then switching fuel lines, etc., until the component causing the problem could be identified.

The condition of the inside of the fuel line, and/or the earlier 1 vent versus later 2 vent carbs would be my first two suspects as the cause of the condition. I sure would like to see an answer, even though I have never had the problem. Most of my driving is at sea level, but I have also driven my car in the mountains of NC and Virginia in hot weather without a problem. There has to be a plausible explanation, but I have no idea what it is.
 
MCHinson said:
steve s,

... I wish the guy with the two Model A's that has the problem and the one without the problem would try switching carbs between the cars, then switching fuel lines, etc., until the component causing the problem could be identified. ...
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The guy, who happens to president of our local club, did the experiment of swapping carbs (but not fuel lines, etc.) and reported result in our latest newsletter: The problem was NOT carb related; vapor lock stayed with the car, not the carb. Must be some subtle difference in air flow patterns in the engine compartments. It's not engine pans; others have reported problems with or without them.

Steve
 
Time to get out the cloths pins.
I know some (maybe all) of you guys just hate me........but ain't it fun!!
 
Giles: Slightly off topic, but here goes: EPA regulates 3 pollutants for gasoline engines: unburned hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx). Oxygenates are compounds such as alcohols and ethers (remember MTBE?) that contain an OH group. Ethanol, for example is C2H5OH chemically. Under ideal conditions, all hydrocarbons will combust to make CO2 and water (H2O) using the equation: C7H16 + 11O2 -> 7CO2 + 8H2O. When an engine is cold the reaction often doesn't go all the way to CO2 but stops at CO (a regulated pollutant). Oxygenates in the fuel "partially oxidize" the fuel molecule by adding the OH and are said to chemically lean because they require less oxygen for complete combustion. They help the reaction go to CO2, thus lowering CO emissions. Racers who use ethanol have to increase the size of their jets to accommodate the "leaner" fuel. Pertaining to this thread, the boiling point of ethanol will have no effect on Marc's problem and I agree with Larry on most points regarding vapor lock. However, because of its volatility characteristics, ethanol depresses part of the distillation curve and THAT could lead to driveability problems under certain conditions. Hope that helps - sorry for the nerdiness :o
 
Old182 said:
With all due respect to Phil and John, and just to set the record straight: First: Ethanol boils at 173F. This is almost in the middle of the distillation curve for virtually every gasoline made (gasolines boil between about 75-80F to a maximum of 437F by spec). Ethanol has its problems, but not as many as we're led to believe. Second: John's hot rodder friend was wrong: The addition of ethanol into gasoline has nothing to do with octane grade. It's added to gasoline to reduce CO emissions by chemically leaning the fuel-air mixture (more info if you want it). If you live in a CO Non Attainment area as defined by U.S. EPA (which I believe Denver and most other large cities are), you have ethanol (or another oxygenate) in every grade of gasoline because it must contain minimum 2.0 weight% oxygen. You can find out if gasoline contains ethanol (or other polar compounds) using a simple test the aviation guys use: Take a small vial and put some water in it. Mark the water level. Add some gasoliine and shake. If the water level increases, alcohol was extracted from the fuel. If not, there was no alcohol there. ;)
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True the ethenol does not effect the octane but it is not blended into the higher rated fuels. So running higher octane gets rid of the ethenol.
 
steve s,

Thanks for that update. Any chance he might be willing to try swapping out some other items, starting with the fuel line? It sure would be nice to have an answer for those who are having this problem.
 
Bob A. said:
Stan, I carry my vapor lock clothes pin wherever I go just in case I encounter this problem.:p
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Thanks Bob, I appreciate a good sense of humor. Also I've never had that "vapor lock" problem on my slightly modified 48 1/2 ton :eek:
 

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John, I respectfully disagree. My statement regarding "...has nothing to do with octane grade..." was meant to point out that its addition to gasolines is for emissions purposes only, mandated by the U.S. EPA, and should you find yourself in a carbon monoxide (CO) Non Attainment area (most big cities), you will, in fact, have a minimum of 2 weight% oxygen in each and every grade of gasoline at the pump, regardless of its octane value. Ethanol has become the oxygenate of choice to achieve this mandate since MTBE was all but banned a few years ago. If you are away from the bigger cities, ethanol may or may not be included in the gasoline. However, ethanol has a Research octane number of 109 and a Motor octane number of 90. This puts the (R+M)/2 value, or Antiknock Index at 100 - it definitley DOES affect the octane value of the fuel, but that's not why it's in there. If a refiner makes sub-octane gasoline knowing ethanol will be added at the terminal to meet regulations AND to boost octane, it only makes sense that if the lower octane grades have it, the higher octane grades would also have it. I may have been unclear previously. No offense meant, but I believe the hot rodder is still wrong.
 
Marc,

Is it possible that you are using gasoline from last winter or have recently filled up from a station with a low volume of gasoline sales? Maybe the station is still selling "winter gas" in the storage tank!

What I am getting at is if the gas you are using is "winter gas" ... it will boil at a much lower temperature and cause vapor lock or vapor bubbles in the system at a lower temperature.

On a 95 degree day recently I opened a 5 gallon GI can of "winter gas" and as soon as I relieved the pressure the gas started to boil and continued to boil in the GI can for 3 or 4 minutes.

Cars with fuel pumps have less vapor lock problems compared to gravity feed systems because of the pressure the pump creates prevents boiling at a given temperature Just like the gas in my GI can did not boil until I relieved the pressure when I opened the can.
 
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Benson said:
Marc,
... Cars with fuel pumps have less vapor lock problems compared to gravity feed systems because of the pressure the pump creates prevents boiling at a given temperature Just like the gas in my GI can did not boil until I relieved the pressure when I opened the can.
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This is only true for modern setups with the fuel pump in the gas tank so it's always pushing on liquid, in contrast to the earlier arrangements with the fuel pump on the side of the motor where it often found itself trying to suck on vapor.

Steve
 
Marc:

I have a 53' Mercury and had the same proublems. I finaly gave up and put a new Carter fuel pump on the car (from MAC's). I mounted it on the frame of the car just in front of the rear wheel.The nice think about the new Carters is that they are set for between 3.5 and 4.5 lbs, so you do not need a fuel regulator. I did put a new mech fuel pump on the car too. When I begin to have proublems, I simply hit the switch for the pump and once the car picks back up, I turn off the switch and continue on with the mech pump. I did a bypass hose around the pump with a check valve from Graingers (they have a store in Denver). The check valve is a perfect fit and cheep.Yes it is not the cleanest instalation (too many hose clamps) but it works great.

Good luck.....
 

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This is important to me because I took my Model A Coupe to the gas station for the first time just yesterday.
Everything was fine on the way into town, only five miles from my garage.
It was a hot day yesterday (91 degrees at the time).
I left the engine running for the fill up since I am a novice with my Model A, just building up some confidence, and I wanted to assure that I would not have problems starting a hot engine.
Well, I filled 'er up to the filler neck for the first time and drove away.
Turning away from the main drag in our little town to avoid traffic, the engine started sputtering and would not run above an idle without stalling.
I found that the only way of having a chance of getting home was at an idle!
Fortunately that little drive-train would pull some pretty good hills at an idle and I am pretty smooth with the clutch and avoided any unnecessary stoppages.
Along the five miles home, I stopped once to check the water in the radiator since the little fancy radiator cap showed red all the way to the top. I added 1/2 gal. of water which I put in the add-on trunk-box for just such an occasion.
Twice the engine did sputter to a stop along the five miles home.
The second time I could hear an air sucking sound since the engine was dead.
I traced it to the fuel filler cap. I thought it funny that a cap, which looked original, would not be venting air the way it should!
I later went on-line and learned from the site "Model 'A' Ford Garage" the difference between Eaton original vented and non-vented fuel filler caps. But, reflecting on the long five mile ride home at an idle, I came to this Vapor Lock 101? thread. Which makes me think that I had a really good case of vapor lock as the primary root cause. The non-venting Eaton cap I believe is a secondary contributing root cause.
This morning in Carthage, NC is was only 69 degrees so fired-up that beautiful Model A Coupe and, voila, no vapor lock at all, full revs, power, the whole shmear!
As I mentioned earlier, I'm a Model A neophite, still clumsy with the spark advance, mixture, choke and all that neat stuff. BUT, in my humble opinion, if it looks like a duck, walks like a duck and quacks like a duck...it's most likely a duck. Blessings to you all and thanks for all of your information in this fascinating thread!
 
joltesvig

I would STRONGLY urge you NOT to fill the Model A with the engine running.

It's very easy to fill up the tank and have the gas pour out on a hot day if your not careful. The gas, being cold from the tank, will expand and can run out the top. It happened to me......

Marc
 
This must be such a frustrating problem. I would think there would only be a few things to check. I have not seen the problem in my car, knock on wood, even in South Florida with ethanol gas.

We know for a fact that vapor lock happens when the gas boils creating an air pocket that stops the gas flow.

Can we start a list of thinks that would cause the engine compartment to get hot enough to cause the problem?

I figure we could create a list and once done, those with the problem could pick the things that their car have via a poll and see if we see anything in common.

How about;

Engine pans - they are supposed to direct air flow across the engine.
Flush radiator regularly?
Plain water or antifreeze - what ratio?
Steel fuel lines, copper lines
Color of plugs - to indicate lean running
Additional fuel filter - I'm thinking fuel would flow at a rate greater than what is used so large amounts of fuel would enter the carb be used valve would open refill the bowl, as opposed to the valve always having to be open with fuel "dripping" in the bowl all the time.
How long driven before the problem appears?
Fuel Octane
Fuel Brand

Remember we list the things first for a day or two then create a poll with all the possibilities and have those wit with problem select all that apply. Hopefully we can find an item or two that stick out.
 
FYI
Here is a link to gasoline stations in the U.S. and Canada that sells gasoline without ethanol. Listed by state, by city. Includes Brand, Octane, Street Address and GPS Cor.
http://pure-gas.org/index.jsp

It seems that cities or population areas below approximately 275K are not mandated to include ethanol in gasoline. There were no large metropolitan areas in Texas that listed ethanol free stations.

Note: 91 octane was listed by many stations as ethanol free. However, their lower/higher ocatne gasoline may contain it.
 
"We know for a fact that vapor lock happens when the gas boils creating an air pocket that stops the gas flow."

Why would an air pocket stop the gas flow? There are no loops or high spots in the fuel line. Why doesn't the air pocket rise to the top of the fuel tank?
 
Mountain Dew;213610 ... Why would an air pocket stop the gas flow? There are no loops or high spots in the fuel line. Why doesn't the air pocket rise to the top of the fuel tank?[/QUOTE said:
Bubbles can be sticky. Did you ever have to jiggle the sink stopper to burp the drain and get it to drain? It doesn't help the bubble rise when the liquid it's trying to flow thru is moving in the opposite direction.

Steve
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steve s said:
Bubbles can be sticky. Did you ever have to jiggle the sink stopper to burp the drain and get it to drain? It doesn't help the bubble rise when the liquid it's trying to flow thru is moving in the opposite direction.

A Model A engine provides an ample amount of jiggle to dislodge a bubble from a gas line.

I'm sorry guys, I not buying any of the vapor lock theories. Vapor lock has never happened to me and it never will because I don't believe in it. I have had a faulty condenser and trash in the fuel tank cause my Model A to act like you described. Since I was sceptical, I looked at other things to find the problem and not write it off as the vapor lock mystery.

I don't think you will find a cure for your vapor lock. I think you can find out why your Model A is not performing like it should. Good Luck!!!!
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