Vapor Lock 101 ?

[marc hildebrant]

Group,

I installed a rebuilt Zenith today on to my 1931 Tudor. I had a tillitson on it originally.

I had not had good power with the car and thought that the tillitson needed to be rebuilt. At Berts in Denver I saw a nice rebulit Zenith and decided to try it.

Today was 100 degree's and I'm at 5000 ft. Water boils at 200 degree's.

When I went out for a road trip, the first 10 minutes were great ! Good smooth power and a real joy to drive. Then, the motor lost power and I needed to turn the GAV a couple of turns to get home. What Happened ?

The temp of the water was 190 and it was hot (100) and sunny.

Tonight, I needed a soft serve ice cream and thought that I would try again. The car ran great...even with a run down the road around 50 MPH. Much more power and real smooth motor. The sun was down and the air temp was in the 80's.

Is the loss of power during the hot day vapor lock ?

By the way, when the motor was running bad, it could idle O.K. and when I checked the spark...I had almost 1/2 inch of spark.

Marc

[old1928fordguy]

What I believe you had happen was indeed vapor lock. Depending where you live I think you will find the gas at the pump contains up to 10 % ethenol plus possibly some other additives.Ethenol boils at a lower temp than the old gas we used to get, and even lower temp with your altitude, 5000 ft.Boiling fuel equals vapor.It is not your car or your carb but probably fuel chemistry.When it gets real hot under the hood here in Denver we have the same problem.Sounds like your carb runs great when it a little cooler.Hope this helps,Phil Turner, Berts Model A,Denver

[marc hildebrant]

Phil,

Looks like it was vapor lock after all then.

Marc

[Brubaker]

Vapor lock may be the eternal "tastes great!;less filling!" debate, but I once had a very knowledgeable 'A' old-timer(I hope that's not offensive) tell me symptoms attributed to vapor lock happen when a caged nut in the exhaust manifold breaks off, and heat is transferred to the carb.

[John LaVoy]

ON the return trip from Texas in 2008 we experienced vapor lock on the sedan while traveling through Colorado. The combination you show was the same we experienced high temps high elevation et. If you switch to higher octaine gas it doesn't have the enthenol and will eliminate the problem. This was a tip from a local hot rod guy that stopped to check us out along the road when we experienced the vapor lock.

[Old182]

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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.

[Larry Brumfield]

Marc, your problem may not have been vapor lock at all.

Is vapor lock a continuous thing even with a continuous, GRAVITY FED, fresh supply of cooler gas going in the carburetor from the tank? I don't think so. The carb and fuel line would have to be really hot for that to happen continuously especially while moving down the road.

Now I have seen a few complaints from people claiming the fuel boiled in their carbs after they turned off their engines on a hot day. If they start up and attempt to leave immediately, the engine will sputter and pop some until a fresh supply of cooler gas flows on in. This makes sense.

Now an engine with a mechanical fuel pump can be a different story especially in a place like CO. on a hot day straining up a steep hill or mountain. The vapor lock typically occurs at the pump itself.

But on a gravity fed system vapor lock does not make much sense in my opinion. The fuel would really have to be heat sensitive even in CO. or higher altitude.

There could have been a tiny piece of dirt or trash temporarily stuck in that carb from Berts and it passed on through.

Drive the car out again along the same route on the next 100* day and see if the problem returns.


Larry B.

[old1928fordguy]

Today in a friends car here in Denver ,air temp 101 degrees,5280 feet,same stock up draft Zenith,car started to run rough,opend GAV and it helped a little.Enough to get it off the road,We cracked the gas line and air came out.Gas could be heard boiling in the carb.After relieving the air lock and a cold wet rag on the carb it ran fine until it heated back up and the same happened again.Took it out for a ride tonight at 80 degrees no problem and ran great for 25 miles.Call it what you like but it seems like vapor lock to me.Phil

[steve s]

Originally Posted by Larry Brumfield

Marc, your problem may not have been vapor lock at all.

Is vapor lock a continuous thing even with a continuous, GRAVITY FED, fresh supply of cooler gas going in the carburetor from the tank? I don't think so. The carb and fuel line would have to be really hot for that to happen continuously especially while moving down the road.
...
But on a gravity fed system vapor lock does not make much sense in my opinion. The fuel would really have to be heat sensitive even in CO. or higher altitude. ...
Larry B.

Larry and Marc,

In case you guys missed the earlier extensive vapor lock thread, here is a link you might find of interest:

http://www.fordbarn.com/forum/showth...k+nonbelievers

While there may be some doubt whether vapor LOCK can occur in a continuous running gravity fed engine, there is no doubt that vapor FORMATION can occur. The earlier thread shows a bunch of pictures of it happening in the top of the sediment bowl with the car idling on a summer day with the hood open. Since the initial boiling point of gasoline is around 100F, some such behavior shouldn't be a surprise. Neither is it far fetched to worry that the process might get out of hand, occur further down in the fuel path (out of sight), and cause rough running or stalling under more extreme conditions. For example, I have observed one of those clear plastic fuel filters installed in the fuel line fill up with vapor and then stall the engine--repeatedly. On the other hand, the car in the pictures barely hiccuped when the vapor bubble would periodically burp on through the system.

What mystifies me is why this is such a problem for some and not for others.

Here's one of the pictures showing the vapor bubble whereof I speak.



Steve

[Larry Brumfield]

Originally Posted by old1928fordguy

Today in a friends car here in Denver ,air temp 101 degrees,5280 feet,same stock up draft Zenith,car started to run rough,opend GAV and it helped a little.Enough to get it off the road,We cracked the gas line and air came out.Gas could be heard boiling in the carb.After relieving the air lock and a cold wet rag on the carb it ran fine until it heated back up and the same happened again.Took it out for a ride tonight at 80 degrees no problem and ran great for 25 miles.Call it what you like but it seems like vapor lock to me.Phil

If that's the case then ALL Model A's in the Denver area won't run on a hot day.

If global warming gets any worse you'll have to find a new business.


Larry B.

[Paul from Maine]

If you have one of those clear, plastic in-line filters with an "air" bubble in it, and you are experiencing vapor lock, get rid of the clear, plastic in-line filter. That might be the cause. Might not be either. If its not, go ahead and put the filter back on.

[gilitos]

Old182: never thought of an oxygenate as "chemically leaning" the mixture but it makes great sense. You hint at more information: I'd like to read about it. Regards, Giles

[old1928fordguy]

Dont know if all Model As in Denver will not run on hot days but many here have this problem.Many have been frustrated enough to switch to a downdraft like a Webber carb and an electric fuel pump and have had NO more problems.I am not smart enough to tell why it is some cars and not others but every summer it has been hapening.Voodo ,or bad carma.Who knows I am only trying to help a guy out if I can.Phil

[Tom Wesenberg]

Originally Posted by old1928fordguy

Dont know if all Model As in Denver will not run on hot days but many here have this problem.Many have been frustrated enough to switch to a downdraft like a Webber carb and an electric fuel pump and have had NO more problems.I am not smart enough to tell why it is some cars and not others but every summer it has been hapening.Voodo ,or bad carma.Who knows I am only trying to help a guy out if I can.Phil

I always had trouble with vapor lock when using 10% ethanol and temps over 80*. I found a local station selling good gas, instead of garbage gas and the problems went away, even in 90* temps.

[marc hildebrant]

Seems to be a complex problem. I'm sure that the elevation (5000 ft) can make the problem worse with the lower boiling point.

I'm wondering just "where" the vapor is occuring.

Marc

[Bob A.]

"By the way, when the motor was running bad, it could idle O.K."
How could a car run good at Idle with Vapor Lock?
Larry B. hit it on the head. Remember guys, I'm a "non believer" of vapor lock in a gravity fed system. Oh by the way I was out with my coupe today here on Long Island N.Y. Temp 92* in the shade very humid and in traffic with 160*thermostat and 50-50 anti-freeze. The temperature gauge never went over 180*

[old1928fordguy]

Mark,Ther have been many Voodo cures for vapor lock from clothes pins on the gas lines to wraping lines with aluminum foil but there have been many in the Denver area who add 1/2 to 1 gallon of diesel fuel per fill up on the hottest summer days .There have been enough reliable people saying it works .I know this will bring out the nay sayers here but it has worked with our so called gasoline here in the Rockies. Again maybe this can help. Phil

[Larry Brumfield]

Originally Posted by steve s

Larry and Marc,

In case you guys missed the earlier extensive vapor lock thread, here is a link you might find of interest:

http://www.fordbarn.com/forum/showth...k+nonbelievers

While there may be some doubt whether vapor LOCK can occur in a continuous running gravity fed engine, there is no doubt that vapor FORMATION can occur. The earlier thread shows a bunch of pictures of it happening in the top of the sediment bowl with the car idling on a summer day with the hood open. Since the initial boiling point of gasoline is around 100F, some such behavior shouldn't be a surprise. Neither is it far fetched to worry that the process might get out of hand, occur further down in the fuel path (out of sight), and cause rough running or stalling under more extreme conditions. For example, I have observed one of those clear plastic fuel filters installed in the fuel line fill up with vapor and then stall the engine--repeatedly. On the other hand, the car in the pictures barely hiccuped when the vapor bubble would periodically burp on through the system.

What mystifies me is why this is such a problem for some and not for others.

Here's one of the pictures showing the vapor bubble whereof I speak.



Steve

Steve, that's quite a thread you were involved in. I was not reading much of the new Fordbarn when you posted so this is the first I've seen of it. Looks like many of them share MY VIEW and at least one with like mind is a bonafide engineer, David Cockey. I didn't read them all.

As you probably know, not all Model A's will have the same engine and engine compartment temperatures. They will vary from one to the next and there are many variables affecting each one. So before any conclusions can be definitively reached with any particular Model A, I think an actual temperature measurement of the fuel should be performed when the suspected vapor occurs. Then contact the makers of the particular fuel and find out the temperature specs. including the vapor pressure, exact boiling point, effect of various ethanol percentages and any other pertinent information necessary to determine its transition to vapor and also exactly when they change from winter to summer gas and back again and the specs. that go with each.

Then with a little effort you will probably reach a most believable and accurate conclusion.


Larry B.

[marc hildebrant]

Originally Posted by Bob A.

"By the way, when the motor was running bad, it could idle O.K."
How could a car run good at Idle with Vapor Lock?
Larry B. hit it on the head. Remember guys, I'm a "non believer" of vapor lock in a gravity fed system. Oh by the way I was out with my coupe today here on Long Island N.Y. Temp 92* in the shade very humid and in traffic with 160*thermostat and 50-50 anti-freeze. The temperature gauge never went over 180*

Bob,

What I believe is that the flow of fuel has been reduced greatly due to the formation of vapor in the line/carb. What I found was that the car would idle, but with the smallest clutch action to drive, it would run very rough.
However, the adjustment of the GAV about 1 to 2 turns richer helped some.

Also, the water temp was around 190.

Marc

[marc hildebrant]

Originally Posted by old1928fordguy

Mark,Ther have been many Voodo cures for vapor lock from clothes pins on the gas lines to wraping lines with aluminum foil but there have been many in the Denver area who add 1/2 to 1 gallon of diesel fuel per fill up on the hottest summer days .There have been enough reliable people saying it works .I know this will bring out the nay sayers here but it has worked with our so called gasoline here in the Rockies. Again maybe this can help. Phil

Phil,

Thanks for the information. Another thought is that we have a lower octane here in the West. I use the 87 type. It may boil at a lower temp ?

Marc