For vapor lock nonbelievers

[Tom Wesenberg]

Yep the "10% crap gas" will likely boil easier than the other stuff available to you, but probably because of the "crap" factor, not the 10% ethanol. More of the unwanted refinery butane gets dumped in the low octane mix, as it does not help the R+M numbers. In Chicago, by Illinois law affecting certain counties, all grades, premium and regular, are mixed with 10% E. I prefer my corn on the cob, but in Chicago that's not the only way you get it. Shucks.

The premium grade Mobil with 10E near me appears to generate less vapor pressure than the regular E10. My lawnmower doesn't care, (damn thing jumps up and wags its tail when I walk in the garage, starts on half a pull) but when I buy the local Mobil reg. in the summer, the unvented plastic 2 gallon gas can I have swells up to a rolly-polly bottom. When I splurge and get premium (50 cents more for two gallons! ) the can behaves in the hot garage. No science, just observation of unknown relevance.

Yep, I've also noticed that my red plastic cans turn into beach balls even when it's not all that hot outside. Yep, the good old days really were better!

 

[Bob A.]

I wonder if anyone with the late Zenith carburetor set up, the one with the side bowl screen filter, has had this problem?

Michael, I read somewhere that the early carburetors didn't have a vent and Henry knew this could cause a problem with the float valve feeding fuel. The carburetor's lower half was modified with a vent hole some time in the '30's. How true? I don't know maybe some one else could verify this.

 

[Tom Wesenberg]

If my dad saw me put a clothes pin on a gas line and I told him it was for vapor lock control, I would have a size 9 shoe up my a**. Dad was a mechanic with his own shop in the late '20's to some time in the '30's.

I agree, the clothespin is a joke as it couldn't absorb much heat, and it wouldn't insulate much with it's small coverage.

One more question needs to be answered about heat and gas. When I had the 10% ethanol gas in my tank I parked at the Twin Cities Ford plant on a hot day. A couple hours later I went to leave and the engine started but dies after a few seconds. Gas wouldn't flow to the carb until I removed the line from the carb and established a good flow. A few hours later it did the same thing when I was parked for a couple more hours. So far it's never done that with the good gas, but I'm not sure that I've had it parked for a couple hours on such a hot day either.

 

[David Cockey]

Michael, I read somewhere that the early carburetors didn't have a vent and Henry knew this could cause a problem with the float valve feeding fuel. The carburetor's lower half was modified with a vent hole some time in the '30's. How true? I don't know maybe some one else could verify this.

Every Model A carburetor has the bowl vented to the atmosphere. They won't work if the vent is completely blocked. Carburetors work based on the pressure difference between the fuel in the bowl and the air going past the hole at the end of the jet.

 

[Stan/MO.]

If my dad saw me put a clothes pin on a gas line and I told him it was for vapor lock control, I would have a size 9 shoe up my a**. Dad was a mechanic with his own shop in the late '20's to some time in the '30's.

I'll have to admit I have several antique motorcycles, and a few antique cars and trucks, and I've never had the dreaded "vapor lock" happen to me. But I've always heard about it, so I can't say it dosen't happen. I'll just keep knockin' on wood.

 

[36 coupe]

Tom I used some white plastic tubing on an Indian motorcycle that had trouble in hot weather usually a stop lights.That was the cure.Years of troubleshooting in mechanics and electronics have taught me to never say never.I have a friend who has been struck by lightning twice.The Model A gas line is very close to the exhaust manifold.

 

[Tom Wesenberg]

Tom I used some white plastic tubing on an Indian motorcycle that had trouble in hot weather usually a stop lights.That was the cure.Years of troubleshooting in mechanics and electronics have taught me to never say never.I have a friend who has been struck by lightning twice.The Model A gas line is very close to the exhaust manifold.

Yep, the white reflects the heat and can make the difference between gas boiling or not in the line and carb. As you say, it's very close to the exhaust and picks up a lot of heat. I carry my plastic cover under the seat in case I need it again. I'll be using the garbage gas again on a trip in a couple weeks, so we'll see.

 

[steve s]

... Yes, ethanol is a lousy add to the blend, but not the major vapor pressure culprit. ...

Mike,

I don't doubt what you're saying about cracking products--not my area. But, I think that the ethanol and butane effects are two sides of the same coin. The way the ethanol-induced positive deviations from Raoult's Law work to increase the vapor pressure is to drive off the hydrocarbons, such as butane. The resulting increase in air pollution due to excessive hydrocarbons driven off into the air was the major challenge the companies had to overcome before they could bring ethanol enhanced gasoline to market. In other words, the problem is not so much vaporization of ethanol but other hydrocarbons that are unhappy cohabiting with the ethanol.

Steve

 

[steve s]

Well written Steve, but you’re going to have to do better. All I see is an air bubble which will be displaced by the fuel tank vent or carburetor vent. ...

I wonder what it would take. Can you tell the difference between an air bubble and a hydrocarbon vapor bubble by appearance? I can't. I do know that there is no physically plausible mechanism whereby that quantity of air could magically appear in that location. Where do you think it comes from? Swim down from the head space of the gas tank? Somehow being sucked in through the fuel line fittings THAT ARE UNDER PRESSURE AND DON'T OTHERWISE LEAK?

Remember, I saw the same thing in that clear inline fuel filter. I could watch it fill up with vapor and then shut down the flow and kill the engine--true vapor lock.

Come to think of it, the only actual Model A vapor locks I've seen have been associated with fuel filters. My own problems are limited to really rough running after long pulls on hot days--textbook vapor lock conditions. I can keep my car running by revving the engine.

Steve

 

[steve s]

... Did the engine "hiccup" at all? I'd be surprised if it did. Once the bubble flowed out of the fuel line into the carburetor bowl it was vented to air through the vent from the bowl to the atmosphere. Remember, fuel does not flow directly from the fuel line into the manifold. The fuel drawn into the manifold is drawn from the fuel in the bowl. The bowl is vented to the atmosphere. As the fuel level in the bowl drops due to fuel being drawn from it the float valve opens and more fuel and and any vapor or air bubbles in the line flow into the bowl. The vapor or air then goes out the vent to the atmosphere. And fuel continues to be drawn from the bowl into the manifold and the engine keeps running..

I watched the phenomenon carefully through many cycles. It was fascinating. Sometimes there was no perceptible hiccup and sometimes there seemed to be a slight unevenness in running. When the bubble is coming into the carb, liquid gas is NOT coming in. Even though the bubble would be vented out, the gas level in the bowl would have to be slightly, albeit briefly, affected. I know that modest changes in fuel level have no observable effect AT IDLE: I see this everytime I close my shut off valve and burn off some gas before parking my car.

What I think my pictures prove is that fuel vaporization can occur in a Model A. The location of my bubble proves that it does not depend on the carb or any other downstream details. It is a reasonable assumption that under more demanding conditions--like, NOT idling in the driveway with the hood up--actual vapor lock can occur.

As I said previously, I do not have actual vapor lock in my car. Under classic, textbook vapor lock conditions (coming to idle after a long pull on a hot day) I get really rough running. I can keep it running by revving the engine. The only actual Model A vapor locks I've personally observed have been associated with a fuel filter. It apparently can trap an impenetrable vapor bubble.

Steve

 

[Kurt in NJ]

I have never had "vapor lock", I have had condenser lock, and ignition coil lock, condenser lock was cured with an A&L condenser, but I did melt the solder holding the grounding tab on (I ran it for years with it bent to make contact) now they are welded on.

This past Memorial day I tried to induce vapor lock ----

1/4 tank of winter gas (NJ xtra water reg)bought in december

85+ degree day, walking speed parade --1st gear, idle speed.

for added heat--cracked exhaust manifold just after #2 --blowing exhaust directly on the carb bowl

It ran fine

Later we went for a drive to Ocean City, on the way back got stuck in traffic for 45 min---the drawbridge was too hot and was being watered down to cool it so it would close --still no problem, but I was worried that I would run out of gas, made it home with no problems, no vapor lock.

I have never seen any bubbles in my sediment bowl -I use a cast iron sediment bowl.

Maybe it is the original late style 2 blade fan --the vibrations from the blades flexing prevent the formation of large fuel blocking bubbles ---or is it the sediment bowl --cannot see any bubbles therefore they do not exist--

 

[steve s]

I have never had "vapor lock", ...I have never seen any bubbles in my sediment bowl -I use a cast iron sediment bowl.

Maybe it is the original late style 2 blade fan --the vibrations from the blades flexing prevent the formation of large fuel blocking bubbles ---or is it the sediment bowl --cannot see any bubbles therefore they do not exist--

Kurt,

I am happy for you and everyone else who has never had vapor lock.

I'm not sure whether you're joking, but do you really think you could see bubbles in a cast iron bowl? X-ray vision?

I was using the plastic fan.

Steve

 

[pat in Santa Cruz]

I wonder if anyone with the late Zenith carburetor set up, the one with the side bowl screen filter, has had this problem?

I have toured in the heat when it was so hot the fuel iin the gas line was bubbling like a percolator. I have an inline glass filter and I could see the boiling vapor rise toward the tank. I could hear it boiling in the carburetor bowl. Gasoline and vapor were venting out the bowl vent. I think the 31 indented firewall style valve does not have the necessary trap for the gas to create an embolism like a firewall mounted sediment bowl does. It all vents to the tank. I had hard starting on a hot engine in 115 degree heat up at Crater Lake last year, but once started, it ran fine. The guys with the 29's and 30's were getting vapor lock that was causing stalls in Napa Valley on the first day. We covered their fuel lines, sediment bowls and carburetor bowls with foil backed foam and their trouble stopped.

 

[Kurt in NJ]

Of course i can not see inside, and also i do not think the the fan blade vibrations have any effect on the fuel system.
Most of the posts about vapor lock mention the glass sediment bowl though.
The fuel flow in the cast iron bowl is different than the glass one ---fuel flows directly into the strainer, and perhaps the screen has larger openings in the mesh --I have never compared them for screen mesh counts.

Maybe we need a poll ---cast iron --glass, vapor lock yes, no.

 

[Tom Wesenberg]

My friend's and my 29 Tudors are both early 1929's with cast iron bowls and we have both had vapor lock problems on hot days with crap gas.

I do like the theory though "I haven't had the problem, therefore it doesn't exist". I haven't experienced a thrown rod, therefore it doesn't exist. My babbit will live forever! I hope

 

[Bob A.]

What the heck does that mean, "walk the walk"?

I also walk on the walk, unless there isn't one.
In that case I try to walk on the grass.

Ask a Vietnam veteran.

 

[Bob A.]

I wonder what it would take. Can you tell the difference between an air bubble and a hydrocarbon vapor bubble by appearance? I can't. I do know that there is no physically plausible mechanism whereby that quantity of air could magically appear in that location. Where do you think it comes from? Swim down from the head space of the gas tank? Somehow being sucked in through the fuel line fittings THAT ARE UNDER PRESSURE AND DON'T OTHERWISE LEAK?

Remember, I saw the same thing in that clear inline fuel filter. I could watch it fill up with vapor and then shut down the flow and kill the engine--true vapor lock.

Come to think of it, the only actual Model A vapor locks I've seen have been associated with fuel filters. My own problems are limited to really rough running after long pulls on hot days--textbook vapor lock conditions. I can keep my car running by revving the engine.

Steve

Steve, Maybe I used the wrong terminology/words "air bubble" But the only vapor lock that I've ever seen was associated /occurred with an external fuel pump on the suction side of the pump.
Maybe this phenomena occurs to people who alter their fuel system in a way from the stock version(by adding filters or whatever). I really don't know but I still believe you're not going to get true vapor lock in a straight gravity feed fuel delivery system.

 

[Bob A.]

My friend's and my 29 Tudors are both early 1929's with cast iron bowls and we have both had vapor lock problems on hot days with crap gas.

I do like the theory though "I haven't had the problem, therefore it doesn't exist". I haven't experienced a thrown rod, therefore it doesn't exist. My babbit will live forever! I hope

Why is it that with all the model A's running around today only a small percentage have this problem? We all use the same crap fuel, run basically the same cars and drive in the same temperatures. What is it that I'm doing, that this phenomena doesn't happen to me.

 

[Bill Goddard]

Dave, What you say about the bowl vent makes sense and I think I read somewhere that was the reason the vent was put in during later production. But not every carb has that hole in the bowl. Mine dosen't and I have been considering putting it in.

 

[steve s]

Dave, What you say about the bowl vent makes sense and I think I read somewhere that was the reason the vent was put in during later production. But not every carb has that hole in the bowl. Mine dosen't and I have been considering putting it in.

Bill,

Are you sure your carb doesn't have a bowl vent? I didn't think it was possible for the float control to work unvented. What model carb is it?

The vent can be easy to not notice. Here's a photo of one on a B carb that's been plugged so it can be rerouted for air filter use. That brass plug up under the flange part of the lower section is where the hole was. More modern carbs have an internal vent passage connecting the space over the float bowl to the air-intake throat of the carb.

Steve