Vaporlock and the ensuing conversations

[RockHillWill]

I experienced what am quite certain was vapor lock this afternoon for the first time in my Model A. I had never experienced it before in the Model A, but it was a seldom experienced situation in racing 'back in the day' during the times between practice and qualifying where we had to sit on pit row for a little time between those two events. While I never personally had an issue, to those that did, it was explained by the Union 76 folks, that the insulation provided around the fuel lines and how it affected the 'heat soak' timing relative to the latent heat of evaporation that was blended into the fuel for that portion of the country. At the time I was in racing I understood a little bit about how the latent heat of evaporation effected the speed of the flame front as it propagated in a wedge shaped combustion chamber, but I always had some timing issues when we ran a hemi motor.

I am not to brilliant in this matter, but as of today, I feel that I did experience vapor lock in that Model A. It was in the low 90's, I run engine pans and have a nice flowing radiator. The problem occurred at four different times, all after I had let the car sit for a half hour or so. After it happened the first time, expecting vapor lock, I wet a paper towel, tied it at one end and wrapped it around the fuel line and wet it with cold water. It started each time and would run up to my normal 50 MPH until I stopped or parked again. Each time I cooled it with water, it would start and run at highway speed until I stopped again. Also, I think that I may have contributed to the issue by the fact my water pump leaks profusely and when I got home I discovered that the Boyce meter was near the top of the gauge.

In doing research on this issue, I noted that there are some that are 100% sure that vapor lock does not exist. I had not thought about that before, so I am a little puzzled that some one could be 100% sure that vapor lock does not exist, but if some one has an idea about what happened to me today, I am sure willing to listen, as I did not like stopping in the heat like I did today.

For those that might be open minded enough to consider that it might be vapor lock, what might be some 'cure' or 'adjustments'?. My only thought so far is to switch to marine gas.

As a side note, I did check for a vented gas cap, but the problem was after sitting, not driving. The car responds well to changes in the spark advance lever, and while it wont go over about 53 MPH, that's all it has ever done. It starts on the first 'stomp', accelerates as it always has and idles very low at idle, so at this time I am not suspecting anything in the ignition, but I am willing to listen to new ideas.

[Patrick L.]

I'm a believer in vapor lock, but in other vehicles, not so much in a Model A.

One question I have is about your fuel line. Does yours have a continuous downward pitch ?

I've looked at a couple with that complaint and parts the fuel line were horizontal or pitched upward toward the carburetor. A little bit of 'warping' to get the line pointing down hill and all seemed fixed. Just curious.

[RawhideKid]

Vapor lock is a real good possibility. The first thing I would check is does the fuel line between the firewall and carb ever turn upward? If it is not an always downward flow, the area where it levels out or turns upward will be where the fuel can stand and boil because of the air pocket above the gas caused by the turn upward.

When all else fails, place a few clothes pins along the length of the fuel line from firewall to carburetor.

Also, change the angles to make it a continuous downward flow.

[Rex_A_Lott]

I have had it happen to me. I have a lot less trouble with non-ethanol gas. Good luck

[Bob Johnson]

I have experienced it several times. I do not think it is a problem with the fuel line getting too hot. IMHO it is the carburetor that gets too hot. It gets hot enough to boil the gas. I have found that the circumstances that contribute to this are: Air temperature over 90 degrees, Using winter gas in the hot weather, Waiting at a stop sign (light) after exiting a freeway when going over 50 mph. I also found that when it happens I could keep the engine running if I opened up the GAV 2 to 4 full turns. After a short distance the GAV could be returned to the normal position. When you come to a stop after exiting the freeway there is a lot of heat built up in the engine. If you have to wait at a stop sign some of that heat gets transmitted to the carburetor. If the carburetor gets hot enough the gas will boil. Especially if it is the winter blend which has a mix which boils at a lower temperature. Opening up the GAV allows more liquid gas to enter the manifold. When you get moving again the cooling from the air movement and cooler gas from the gas tank will cool down the carburetor and the GAV can be closed.

The above is what works for me. Your experiences may be different.

Bob

[Y-Blockhead]

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Originally Posted by RockHillWill

...if some one has an idea about what happened to me today, I am sure willing to listen, as I did not like stopping in the heat like I did today.

I believe, in my instances anyway, that when I would stop the carb would heat up and the gas boils. I started shutting off the gas when parking and let it run out of gas. Seems to help. Then I installed a 1/8" phenolic spacer between the carb and manifold to insulate the carb from the heat. That seems to have cured my problem as I have not had "vapor lock" since.

[Vic in E-TN]

Do any of the regular suppliers sell phenolic spacers? I saw some at a swap some years ago but not for a model A. I guess that I would just use a pair of regular paper gaskets. This should significantly reduce the heat transfer from the intake manifold to the carburetor.

Vic

[updraught]

A bit of reading (from back in the day) on the causes of vapour lock on a Winfield S carb that came out in 1930.

Long narrow passage ways in the carb and a lack of insulation ...

http://i.ebayimg.com/images/a/T2eC16...~~/s-l1600.jpg

[Tom F OHIO]

You said the water pump was leaking water very bad and that your meter was at the top of the meter, so could it be possible that you were over heating with the loss of water.

Tom....

[Y-Blockhead]

Originally Posted by Vic in E-TN

Do any of the regular suppliers sell phenolic spacers? I saw some at a swap some years ago but not for a model A. I guess that I would just use a pair of regular paper gaskets. This should significantly reduce the heat transfer from the intake manifold to the carburetor.

Vic

Vic, I got my Phenolic spacer off of epay...

Just went out and grabbed a picture. And sorry, I misspoke. It is a 1/4" thick.

[MAG]

Posts 1 and 5 describe the problem exactly as I have experienced ever since Ethanol gasoline was forced upon us. When the ambient temperature is below 80 degrees I never have a problem. On a recent trip to Big Bend the problem showed up in the afternoon with temp. near 90. I poured cool water in a bowl attached to the fuel filter bowl on the firewall and was able to continue on my way. I have seen the fuel boil in the filter bowl many times.
With non Ethanol fuel I never experience the problem. In the 50's my brother and I drove a '31 Coupe for years without ever having this trouble.

[Benson]

Will,

These are a few thoughts that might help if any of these conditions exist.

1. First off it would help to fix the leaking water pump. If it is leaking as you say it will suck air into the cooling system at speed and as you know it is not good to have air in cooling system. Also if it leaking the coolant level is too low ... see below.

2. When the engine is turned off and allowed to sit as you describe the Model A cooling system is designed to continue cooling the engine during the "Hot Soak" period by making use of Thermosyphon action just like the Model T which has no water pump.

Many people insist on running the coolant just above the tubes at the bottom of the upper tank in the radiator.

Here is why this not a good idea:

This level is BELOW the BOTTOM of the water inlet tube to the radiator so as the hot water tries to syphon up the upper radiator hose it cannot flow into the radiator.

At this point the thermosyphon action is prevented because there is no coolant to continue to circulate (just an air pocket) and the cooling effect is stopped and your engine does not get the cooling effect. Now under hood temperatures go up also. Which can boil the gas in the carb and fuel lines.

3. Also I would follow Service bulletin P 450 on subject of losing coolant out the overflow tube. The overflow pipe MUST be all the way to the rear and Must be as high in the filler spout as you can get it. I solder mine to the rear lip of the filler spout with opening UNDER the lip.

Just because your radiator is new does not mean the overflow is in the correct position!

The idea is to prevent the coolant level from going down to a point where thermosyphon is not possible.

4. Something is amiss if car will not go over 50 MPH at 700 feet in altitude ... my first guess would be lean carburetor mixture or timing maybe.

Most carbs were setup at Factory to run the GAV at 1/4 turn off the seat at sea level and on a level grade. Running with GAV closed is too lean ... especially at or near sea level.

I believe Ford said to increase GAV 1/4 turn to about a 1/2 total or so under a long hard pull... like mud or sand or uphill.

If your engine is still hot enough to vapor lock at 1/2 an hour after shutdown, the above items should help the situation.

If you live where the vapor pressure of gas is increased during winter then it will boil like crazy at 130 degrees ... like if your car still has winter gas in the tank.

FWIW Around here the winter gas boils at about 100 and with SUMMER it boils at about 140.

[BILL WILLIAMSON]

Most likely just gas, boiling in the carb. That creates a "vapor lock" of sorts & gas can't flow into the carb.
Bill W.

[steve s]

https://www.fordbarn.com/forum/showt...teve&showall=1

If you use this website's search function, you'll find numerous earlier threads on the subject. Here is a good thread, which contains (in my comments) links to even earlier threads. Two of the bogus arguments against the existence of vapor lock most frustrating for me are (1) because fuel pumps used to be common sites of vapor lock, now, unless the problem can be traced to a vapor bubble in a fuel pump, it's not really vapor lock, and (2) because liquid normally flows downhill, it's impossible to have vapor lock in a vented, gravity-fed fuel system--in spite of the fact that I routinely see just such blockage in my bathroom sink until I jiggle the stopper to release an air bubble to allow free flow to resume--in a vented, gravity fed system!

[RockHillWill]

All good ideas, guys, thanks for taking time to reply. I am getting a better understanding of a few issues and have a number of ideas that I will try.

Marine gas and a heat 'spacer' between the carb and the manifold will be my first try after I get the water pump replaced. I have a new leak less pump, but this Bugatti project has gotten way out of hand and I have not found much time for other projects. I make the drawing in South Carolina, get the parts cut in North Carolina, and we build the fenders and the frame in Tennessee, and are chasing parts all over the world it seems. I am also tied up making a replica of an M2 50 cal. to mount on the turret of a Humvee M1025 project that is building up steam as a project. Retirement is not all that it's cracked up to be!!! I keep thinking that I have all this 'free' time and take on too many projects.

However, I am still struggling to understand the thought that the 12" or so of head pressure in the gravity fuel system of the Model A has more resistance to an 'air bubble' than that generated by a fuel pump, given the fact that a clogged vent in the gas cap can generate enough vacuum to disrupt fuel flow. I haven't given it much thought, so maybe a good nights sleep or two will help me figure it out.

Fuel boiling in the carb seems to be a real possibility for the problem that I encountered today. Again, thanks to each of you that took the time to respond.

[Big hammer]

I don't know if I have ever experience vapor lock, if my car won't start in a couple of cranks hot, I just pull the choke and it would start? If fuel boils in the carb wear does it go, out of the bowl vent, then the level lowers and fresh fuel replaces the missing fuel? IF the vent is plugged the fuel vapor wouldn't have anywhere to go causing a blockage, or even when the float vavle opens, flow backwards in the fuel lines?
No start engine hot, anyone else just pull the choke and hold it until it starts?
I think I read this or was told this a long time ago, it may not have been model A info !

[Bob Johnson]

If you watch water boiling in a pot you will see that the bubbles (vaporized water) are formed at the bottom of the pot. In a carburetor bowl the inlets for the jets are at the bottom of the bowl. When the fuel in the bowl boils some of the fuel bubbles (vaporized fuel) will enter the jets and the fuel/air mixture will be way too lean.

Bob

[w.michael]

RHW,
Exactly what occurs when you experience vapor lock? You say it happens after you let the car sit for one half hour or so, but what happens? It won't start? Or it starts and dies? I'm just trying to think through what is going on.

W. Michael

[Richard in Anaheim CA]

When know the weather will be hot, I fill a squirt bottle with clean water to take along.

If she starts buckiin and kickin, I pull over, open the hood and give the carburetor, line and filter bowl a few good shots, close the hood and take off.

It usually works well if you can keep the speed of the car up. Haven't had it happen when parked but should work the same.

Richard
Anaheim CA

[RockHillWill]

W.Michael: I made four stops yesterday that lasted from 10-20 minutes, It would start fine, run good for about 30 seconds then began sputtering, popping and on one occasion, a loud 'backfire'. On two occasions, the motor died completely. After the first incident, I wrapped the fuel line in a wet paper towel and it started on the second try and ran well until I made another stop. Each time I had an issue, I would repeat the process with the same results. However, at the last 'stop', I poured some water on the top of the carburetor and it was by far the longest lasting and I made it home, making me believe that my issue was in the carb, not the fuel line. I further contributed to the problem by not noticing that I was running 'hot'.

I am still not clear about why some think that you can not have 'vapor lock' in a Model A. I am willing to change my mind, but won't do so until I understand it. One thing that I may be missing is that I do not know how much the 'head pressure' is in the gravity fed fuel system vs the pressure derived from having a fuel pump. My first thought is that having a fuel pump would generate more fuel pressure. My recollection is the definition of vapor lock is the amount of heat and the resulting pressure from the conversion of a liquid to a gas. The carb atomizes the fuel, but it is still a liquid until it is subjected to the ignition in the combustion chamber, and then the degree to which the fuel has been blended will determine how fast the fuel burns and the pressure builds up.

Again, just thoughts.

[George Miller]

I use to have trouble with vapor lock on my 1928 Sport coupe on hot days here in NC. But some times in early spring on a warm day it would happen. I think it was some winter blend left over that was late getting used up. In the sumer time I think mine was caused by the exhaust manifold heater. I ended up insulating the gas line and using a phenolic spacer.

I'm still going to call it vapor lock.

[Jacksonlll]

The gas is boiling in the carb bowl, leaving you with just vapor. The water bottle is the trick. It fixes it until some cooler fuel gets into the bowl. There is no vapor lock. You are just boiling fuel.

[Benson]

Originally Posted by Big hammer

I don't know if I have ever experience vapor lock, if my car won't start in a couple of cranks hot, I just pull the choke and it would start? If fuel boils in the carb wear does it go, out of the bowl vent, then the level lowers and fresh fuel replaces the missing fuel? IF the vent is plugged the fuel vapor wouldn't have anywhere to go causing a blockage, or even when the float vavle opens, flow backwards in the fuel lines?
No start engine hot, anyone else just pull the choke and hold it until it starts?
I think I read this or was told this a long time ago, it may not have been model A info !

Yes I have noticed in hot weather it is necessary to use the choke on hot starts.

I use car for short trips year round with 10 to 20 minute stops in the middle of the 5-10 mile trips. If cool outside short choke pull is not needed very often.

[steve s]

Originally Posted by RockHillWill

... One thing that I may be missing is that I do not know how much the 'head pressure' is in the gravity fed fuel system vs the pressure derived from having a fuel pump. My first thought is that having a fuel pump would generate more fuel pressure.....

The original fuel pumps were mechanical and worked by creating a vacuum that pulled the fuel from the tank, rather than increased pressure that pushed the fuel. The vacuum, of course, lowered the boiling point of the fuel and, together with the increased temperature in the engine compartment, promoted vaporization of the fuel in the pump such that the pump's mechanism no longer had a grip on the fuel and fuel flow ceased.

Electric fuel pumps might be of a type that either sucks or blows, but the modern arrangement is to submerge a "pusher" style pump in the fuel tank, where it is kept cool and the increased pressure all along the line to the engine prevents premature vaporization.

Since mechanical fuel pumps were the traditional location of a vapor bubble that shut down fuel flow, i.e., "vapor lock," some people feel that you cannot have "true" vapor lock without such a pump. I prefer a more general definition of the problem, including any situation where formation of a fuel vapor bubble either shuts down fuel flow sufficiently to kill the engine or merely slows fuel flow enough to cause rough running, hard starting, etc.

At one time, I installed a clear plastic in-line fuel filter in the middle of my fuel line between the sedimentation bowl and the carb. With the engine idling in the driveway, I could watch the filter almost magically fill up with vapor until flow was impeded sufficiently to stop the engine. I see no reason that this shouldn't qualify as vapor lock, whether it occurs in the sedimentation bowl, a fuel filter, or the carb.

Similarly, I don't think it matters whether the fuel has boiled away, i.e., formed vapor bubbles either from the liquid's interior or where it contacts a hot surface, or the fuel has merely rapidly evaporated from it surface; either way, it is undergoing unwanted and troublesome transformation from the liquid to vapor phase.

[BILL WILLIAMSON]

"TRUE" vapor lock is an area of HIGH pressure vapor, ahead of the fuel pump, that's HIGHER than the pumps' output!
There's been PAGES & PAGES of arguments about what VAPOR LOCK, IS & ISN'T---LOL
Boiling gas in a Model A carb produces such a HIGH pressure area, that gas CAN'T flow to the carb!--"Sometimes we see it blurping through the sediment bowl, tryin' to ESCAPE, back to the TANK!
Bill Clarify

[Y-Blockhead]

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Originally Posted by steve s

I prefer a more general definition of the problem, including any situation where formation of a fuel vapor bubble either shuts down fuel flow sufficiently to kill the engine or merely slows fuel flow enough to cause rough running, hard starting, etc.

At one time, I installed a clear plastic in-line fuel filter in the middle of my fuel line between the sedimentation bowl and the carb. With the engine idling in the driveway, I could watch the filter almost magically fill up with vapor until flow was impeded sufficiently to stop the engine. I see no reason that this shouldn't qualify as vapor lock, whether it occurs in the sedimentation bowl, a fuel filter, or the carb.

Similarly, I don't think it matters whether the fuel has boiled away, i.e., formed vapor bubbles either from the liquid's interior or where it contacts a hot surface, or the fuel has merely rapidly evaporated from it surface; either way, it is undergoing unwanted and troublesome transformation from the liquid to vapor phase.

Great write-up, Steve S. Bottom line is the fuel is boiling and you need to cool it (or keep it cool in the first place). Does it matter if we are using the correct terminology? The installation of a Phenolic Spacer worked for me.

I honestly can't see me jumping out of the car and spraying water on the carb every time it happens... maybe I can get my wife to do it.

[40 Deluxe]

Is the 'no start' from lack of fuel ("vapor lock"), or ignition failure (overheated coil or condenser)? Simple test: Place your hand on top of a couple spark pugs and push the starter rod with the other hand (ignition on). If it bites, you have spark. Cool the carb with water and be on your way!

[mshmodela]

Question when your car would not run, did it have a strong spark? I ask because I wonder if a heat sensitive coil might mimic vapor lock?

[BRENT in 10-uh-C]

Have y'all ever heard the story about the Pontiac owner's car that didn't like Vanilla Ice Cream. True story.

With regard to calling it by its proper name, I think it is very relevant to use the correct terminology. Would you like me to 'remove' the transmission from a Model-A, --or 'pull' the transmission out of a Model-A? Another analogy where the terms have different meanings is Overhauling and Engine vs. Rebuilding an engine. This topic has been (heatedly) discussed many times here in the past, and while a Model-A engine is very susceptible to fuel percolation, in stock form you just will not see Vapor Locking due to exactly what has been mentioned above..

[w.michael]

The reason I asked for more detail on what was happening is that your experience is similar to, but not the same as, my experience. I was convinced my car was vapor locking, but in fact it was the float valve sticking in the closed position. It did happen most often in very hot weather and when the engine was hot, which contributed to my conclusion of vapor lock. The difference is, my car would stall after stopping at a stop sign or stop light and then accelerating through the intersection. It would stall just about the time I shifted into high gear. Yours sounds like it happens after stopping for some period of time, enough time for the heat to build up in the carb/fuel line.

As Mike says above, other conditions can mimic vapor lock. But that doesn't mean vapor lock does not happen.

W. Michael

[stewwolfe]

I was absolutely convinced that I was experiencing vapor lock in my roadster a few years ago. When it was over 85 and I tried to restart the car after less than 15 minutes, it wouldn't start. I would open the hood, and cool the fuel line with wet rags, and it would start. I found out later that I had a intermittent coil. When the temperature got too high, the coil wouldn't put out enough juice to fire the engine. I was cooling the coil by leaving the hood open and cooling the fuel line. I replaced the coil and my "vapor lock" problem disappeared, in three years it hasn't recurred. This is just what happened to me.

[Dick Steinkamp]

The boiling point of gasoline is 102F. The boiling point of ethyl alcohol is 173F.

http://www.firehouse.com/article/105...r-is-it-part-2

Contrary to popular belief, the higher the ethyl alcohol content, the less you will experience vapor lock.

[steve s]

Originally Posted by Dick Steinkamp

The boiling point of gasoline is 102F. The boiling point of ethyl alcohol is 173F.

http://www.firehouse.com/article/105...r-is-it-part-2

Contrary to popular belief, the higher the ethyl alcohol content, the less you will experience vapor lock.

Dick,
It's not that simple. Liquids composed of two dissimilar molecules commonly exhibit "nonideal" mixing (not obeying Raoult's Law). This can result in mixtures having either higher or lower boiling points than either of the two pure components. The nonpolar hydrocarbons of gasoline and the polar ethanol molecules are an example of the latter. In effect, neither of these types of molecules wants to be in intimate contact with the other type.

This, in fact, presented a major technological hurdle for the oil companies when they first were tasked with adding ethanol. The increased volatility of the lighter hydrocarbons in the presence of alcohol created an unacceptable air pollution problem because they lead to photochemical smog.

Further confusing the issue is the fact that gasoline does not have "a" boiling point; it has a boiling range. As the lighter molecules are boiled off, the boiling temperature gradually rises.

Steve

[Dick Steinkamp]

Originally Posted by steve s

This can result in mixtures having either higher or lower boiling points than either of the two pure components.

Thanks, Steve.

So...boiling point of E10?

[steve s]

Originally Posted by Dick Steinkamp

Thanks, Steve.

So...boiling point of E10?

I don't know off hand; I would have to Google it. What I would be expecting to find is an INITIAL boiling point and a boiling RANGE. Also, I would not be surprised to find a set of boiling data for the several different seasonal blends that are sold. For example, the so-called "winter" blend has a higher composition of the lighter fractions, such as propane and butane, and will have a relatively low initial boiling point. I suspect there are also regionally specific blends. For example, the hydrocarbon volatility issue is more critical in California, where smog is a major problem.

[Dick Steinkamp]

Originally Posted by steve s

I don't know off hand; I would have to Google it. What I would be expecting to find is an INITIAL boiling point and a boiling RANGE. Also, I would not be surprised to find a set of boiling data for the several different seasonal blends that are sold. For example, the so-called "winter" blend has a higher composition of the lighter fractions, such as propane and butane, and will have a relatively low initial boiling point. I suspect there are also regionally specific blends. For example, the hydrocarbon volatility issue is more critical in California, where smog is a major problem.

Good points. I would suspect that the lighter fractions of gasoline are present in various quantities depending on the seasonal (or other) blends. It is these lighter fractions of gasoline that are going to vaporize first...no matter how much ethanol is in the fuel mix. And it is these vaporizing gasoline fractions that can (and do) cause vapor lock.

I do remember vapor lock as being a common occurrence in the 50's, well before ethanol was introduced.

[BILL WILLIAMSON]

WHY do we spend so much time, trying to PROVE that Model As VAPORLOCK? Lets just admit there's a problem & try to discover HOW to prevent it, or learn how to deal with it, when it happens?---When gassing up, opening the R/H hood, "might" help keep the carb somewhat COOLER???---I'm going to BED!
Bill Tired

[Kevin in NJ]

Originally Posted by BILL WILLIAMSON

WHY do we spend so much time, trying to PROVE that Model As VAPORLOCK? Lets just admit there's a problem & try to discover HOW to prevent it, or learn how to deal with it, when it happens?---When gassing up, opening the R/H hood, "might" help keep the carb somewhat COOLER???---I'm going to BED!
Bill Tired

Well the first thing you have to do is establish what is happening.

Vapor lock is a condition the happens where a fuel pump can not pump through a fuel vapor bubble in the line. This does not happen in a gravity delivery.

So we can throw out that idea right off.

So what is happening.

First off let us apply logic. A tour goes out in identical conditions with maybe some minor differences in the fuel. Only a car or two has problems, it is not a general big problem with the A. So quickly we need to ask what is different in the cars that have problems?

Here is where things get tricky. As pointed out by an earlier post often it is electrical like a bad coil. But in reality is can be a combination of small things. One person told me about years of vapor lock under certain conditions. When the engine came apart for other reasons it was discovered the valve lash was border line on a couple of cylinders and when things got hot enough the metal expanded enough the valves could not seal.
So imagine an engine with rust in the water jacket, a slightly lean carb and someone that does not know how to advance the spark. Things get warmer than they should and the temps go up some and now the carb starts boiling.

There are many combinations of small things that can add up to troubles under some conditions.

The key to remember is most A's do not have problems. So if you are having a problem a band aid might be a insulation block, but the true fix is something else. Just a question if you have the experience to find the problem.
Please understand I am not knocking people for being inexperienced. Just there are some people that know stuff and can take a quick look an usually see the problem. Others that just have not have the experience to know how to fix the subtle problem.

The road to a proper repair starts with acknowledging you have a problem that can be properly fixed. If you just settle with "I have vapor lock and that is just a problem with the A's" then you have lost all hope. In reality you have to start asking more difficult questions and take the time and hard work of tracking down the real problem.

[steve s]

And now we have come full circle.

[RockHillWill]

Jeez, guys, what's the big deal here???? When a liquids is changed to a gas it is vaporized. It makes no difference if you have a fuel pump, a gas tank 10 feet tall or a carburetor too close to the heat. If the fuel stops flowing because of vapor ANYWHERE, caused by ANYTHING, the darn thing is vapor locked!

[Kevin in NJ]

But if you have fuel purculating in the bowl forcing the float up preventing fuel flow is that vapor lock?

[George Miller]

Originally Posted by RockHillWill

Jeez, guys, what's the big deal here???? When a liquids is changed to a gas it is vaporized. It makes no difference if you have a fuel pump, a gas tank 10 feet tall or a carburetor too close to the heat. If the fuel stops flowing because of vapor ANYWHERE, caused by ANYTHING, the darn thing is vapor locked!

Plus 1 I'm with you.

[Dick Steinkamp]

Webster's says vapor lock is...

"partial or complete interruption of flow of a fluid (such as fuel in an internal combustion engine) caused by the formation of bubbles of vapor in the feeding system"

https://www.merriam-webster.com/dictionary/vapor%20lock

[Dick Steinkamp]

Originally Posted by Kevin in NJ

But if you have fuel purculating in the bowl forcing the float up preventing fuel flow is that vapor lock?

I'm not sure how the fuel vaporizing in the float bowl would force the float up. Isn't the float bowl vented?

[Gold Digger]

I know this, I had a 29 that the engine would die driving down the road and I would loosen the gas line at the carb and steam would spew out for a second or two then liquid would run out. I could restart and go for a few miles and same thing again. Put 4 cloths pins on the line and it never occurred again. Thinking back that car had a copper gas line on it and I wonder if that may have contributed to the problem.

[steve s]

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Originally Posted by Dick Steinkamp

Webster's says vapor lock is...

"partial or complete interruption of flow of a fluid (such as fuel in an internal combustion engine) caused by the formation of bubbles of vapor in the feeding system"

https://www.merriam-webster.com/dictionary/vapor%20lock

No fair, Dick!

[Big hammer]

Very interesting thread! My post when my A would start hot, i pull the choke and it starts !
With my riding lawn mower I also find the same thing, running it hard, then stop for a break, if it won't start hot, I pull the choke, it starts and I'm back mowing! Should I fix a problem or just get it running again as quickly as possible? One of the advantages of having a manual choke!

[RockHillWill]

Man, it's been a long time, since I've had this much fun!!!

Yes, If vapor is contributing to the stoppage of fuel flow it is vapor locked.

If you don't not have a key, does it really matter what kind of a lock it is????

[CT Jack]

3 possible causes for fuel flow related problem:
1. Fuel contaminated with water
2. Ethanol vaporizing causing poor to no flow of fuel to engine
3. Carburetor has a marginal high speed jet flow rate. Low flow is restricting higher engine speeds. Float level needs adjusting
Solution for 1 & 2 - empty fuel tank, install 89 or 93 grade gas, and add some Marvel Mystery Oil to fuel.

[Tom Wesenberg]

Originally Posted by George Miller

Plus 1 I'm with you.

Plus 2

I used to think vapor lock couldn't happen in a gravity feed system until it happened to my friend while I was riding with him, and then a couple weeks later it happened to me in my 28.

It even happened on a hot day while the car was parked for 3 hours, and all the fuel boiled away in the carb and fuel line. I turned the tank valve back on, but fuel wouldn't start flowing until I removed the line at the carb, then I reconnected it and drove away. This same thing happened twice in one day.

[bobbycoke]

My pop was a Ford employee in the late 30's and early 40's after the war was a Ford dealer service manager and twice we had vapor lock on vacation in his 1953 Ford [his first new car he bought because they were doing away with the flathead the next year] when in the southwest with real hot temps..........first time was near a lttle fruit and veggie stand......he walked over while car cooled [as much as it could in 100 degree weather ] got 2 grapefruits cut them halve way through and straddled the fuel line with them by the carb.........no more Vaporlock that day !!!!!!!!!!!! The next time it happened [another southern vacation] he went to the trunk and pulled out a package of wooden clothespins [the spring type ] and put them the fuel line another cheap "heat sink" that really impressed a 7-8 year old kid who knew Dad could fix anything with nothing!!!!!!!!!! He had planted the clothespins for suck an occasion.........LOL .......great memories brought up by this thead.......bobbycoke

[steve s]

Whenever I find myself feeling too mystified about how some people can deny vapor lock can occur in a Model A because they've never personally seen it, I try to remind myself that that's how I feel about the clothes pin thing. How can that possibly work!? Wood is a terrible heat conductor and heat sink. But a lot of people swear by it.

I would point out, however, that the clothes pins (or the grapefruit halves) are applied to a fuel line, not a fuel pump.

[Benson]

...

[stouchton]

Good article below.... fact checked as much as I could at lunch time and seems to check out well.

Also - ethanol fuel will burn leaner, engine runs hotter - contributing to the problem.

Noticed the leaner condition on an engine I was setting up using an air/fuel meter. Actually changed the main jetting based upon type of fuel. So... on the A you probably could compensate with the GAV - I never tried this when I had an issue. Removing my thermostat solved my problem, and I can run E10 though the engine has more pep on the straight stuff!!!

http://www.militarytrader.com/milita...other-gas-woes

[Flathead]

How about this?? What if you soak the wooden clothes pins in water first, then when you clamp them on the fuel line the water evaporating from the wood will give an extra boost to the cooling effect. Armchair scientists may now chime in.

[steve s]

Originally Posted by Flathead

How about this?? What if you soak the wooden clothes pins in water first, then when you clamp them on the fuel line the water evaporating from the wood will give an extra boost to the cooling effect. Armchair scientists may now chime in.

I'm not sure if you're serious or not, but in case you are--and speaking as an actual scientist but an armchair mechanic--the water would not only give an "extra boost to the cooling effect," but would constitute the totality of the cooling effect. Of course, because wood doesn't absorb much water, the effect would be very short lived. I've never seen anyone who claimed that the clothes pin trick worked mention the need to first soak them.

[RUNNERBUN]

The thing I see that all arguments have in common is "HEAT" and "HIGH TEMPERATURE" Be it called Vaporlock. Boiling Carb or any other name you may wish to use, the effect is the same. Rough running engine, lack of power or just plain stopping alltogether.
I experienced the problem for the first time after I had run up a total of over 80,000 km and did not believe the problem was vaporlock. Removed Carb from the car several times to do a complete inspection and found nothing out of place. Each time when I reinstalled the Carb it ran perfectly until the engine got up to temp again. I then tried lightly spraying the Carb with water when I came to a stop and the problem was fixed.
I therefore concluded that the problem was indeed caused by overheating of the Carb and also possibly contributed by the unknown quality of the fuel as I was at the time travelling away from my home State and at best some fuel is of suspect quality.
I live in the tropics so I'm no stranger to high temps. yet I never experienced vaporlock???? while driving at home. Just my 2 cents worth.

[DC 69]

Related to ethanol, vapor lock, and just thought I would ask: Has anyone thought of using AV-Gas (aviation fuel)? Pros vs Cons, etc.

[RockHillWill]

For those that still don't believe in vapor lock:

https://sciencing.com/two-types-vapo...n-8676696.html

[Benson]

Originally Posted by DC 69

Related to ethanol, vapor lock, and just thought I would ask: Has anyone thought of using AV-Gas (aviation fuel)? Pros vs Cons, etc.

There is a hefty fine for using AV Gas in a car driven on public highways!

There is no road tax on AV gas and the Department of Revenue gets POed when they find out that you are driving on public roads and NOT paying Road Tax.

[carolinamudwalker]

They are adding BUTANE to our gas now to get rid of it. Before the EPA the refineries just burned it off It only causes problems in an open fuel system as in carburetors. The zenith carb is cast iron and obsorbs a lot of heat. The after market carbs like the tilli not so much. The 1/4 inch spacer should help.

[sjhark]

My first car was a 1975 Plymouth Duster that I shoehorned a 383 big block that took up every inch of the engine bay. Man, did it heat up! I ran a 4 barrel Holley and had a lot of problems with vapor lock. I fixed the problem with an aluminum plate heat shield and a phenolic spacer between the carb and the heat shield. I wonder if a similar setup, with the shield running down between the engine and carb, would work...

[steve s]

Originally Posted by carolinamudwalker

They are adding BUTANE to our gas now to get rid of it. Before the EPA the refineries just burned it off It only causes problems in an open fuel system as in carburetors. ....

To the extent that butane (C4H10) is being added to gasoline, it's not likely to get rid of vapor lock. On the contrary, it would be added in winter time to INCREASE the volatility (lower boiling point/increase vapor pressure) to help with cold-engine starts. In the summer time, such low molecular weight hydrocarbons will promote vapor lock, and even more so in the presence of ethanol, which tries to drive the more volatile hydrocarbon fractions out of the liquid into the vapor phase.

[Crankster]

I believe he's saying they add Butane to gasoline to get rid of it in the sense it's sort of a waste product, not that it does anything good for vapor lock.

The wooden clothes-pin trick works, though as I understand it not due to any heat sink action. They act as insulators.

[daren007]

Just open the hood for a few minutes after stopping until you get this problem sorted out. If you are using todays fuels you will have problems when the engine heat soaks.

[steve s]

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Originally Posted by Crankster

I believe he's saying they add Butane to gasoline to get rid of it in the sense it's sort of a waste product, not that it does anything good for vapor lock.....

Upon re-reading, I think you're right about what he meant--the "it" was butane, not vapor lock.

Ideally, all of the butane and other fractions that must be flared away could be incorporated into useful fuel. However, I believe that the addition of ethanol to gasoline, if anything, has decreased the amount of butane that can be included because of ethanol's effect of increasing gasoline's vapor pressure. As ethanol itself has a lower vapor pressure than gasoline, this is quite counter-intuitive.

[Mike V. Florida]

Why doesn't the bubble just travel back up to the tank?

[RockHillWill]

The pressure differential will determine the direction of travel.

[steve s]

Originally Posted by Mike V. Florida

Why doesn't the bubble just travel back up to the tank?

Even bubbles can be sticky--why not?

Examples of such metastability are all around us--lots of things that "should" happen either happen immeasurably slowly, or erratically and unpredictably, or not until it's given a tickle of some sort, or maybe not at all. My favorite example is the fact that the organic world and its inhabitants, bathed in a sea of oxygen as it is, doesn't burst into flames, as would be predicted if things were as simple as energy (i.e., "should") being in charge.