Vaporlock and the ensuing conversations

[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!