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.