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Old 05-30-2012, 04:44 AM   #41
BRENT in 10-uh-C
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Default Re: Vapor lock!

You know, it should make 'one ponder just why this topic of "vapor lock" is so controvercial. If you think about it, even float-a-motor mount or motor oil discussions here do not create the stir like this topic does. It is almost like folks want to fight about it to prove it can, -or cannot happen to them!! I find it even more ironic that apparently if someone raises the octane level of the fuel in the tank, the issue seemingly goes away?

The other thought I ponder is folks are basing this issue now on the ethenol laced fuels. Back a few decades ago when vapor lock was an issue, what was the blame then? Ethenol fuel??
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Old 05-30-2012, 05:01 AM   #42
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Default Re: Vapor lock!

Quote:
Originally Posted by BILL WILLIAMSON View Post
In modern injected cars, excess pressure is routed back to the tank, therefore the fuel is always flowing in a loop from & to the tank & runs somewhat cooler gas temperature.
If I ever experience this so called "vapor lock," I think I would put a nipple in the carb screen plug, run a hose into a hole drilled in an old gas cap as a way for air bubbles or vapor pressure to escape back to gas tank. Bill W.
Excluding anything except normally aspirated cars .

Last edited by James Rogers; 05-30-2012 at 05:16 AM.
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Old 05-30-2012, 05:15 AM   #43
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Default Re: Vapor lock!

Quote:
Originally Posted by BRENT in 10-uh-C View Post
You know, it should make 'one ponder just why this topic of "vapor lock" is so controvercial. If you think about it, even float-a-motor mount or motor oil discussions here do not create the stir like this topic does. It is almost like folks want to fight about it to prove it can, -or cannot happen to them!! I find it even more ironic that apparently if someone raises the octane level of the fuel in the tank, the issue seemingly goes away?

The other thought I ponder is folks are basing this issue now on the ethenol laced fuels. Back a few decades ago when vapor lock was an issue, what was the blame then? Ethenol fuel??
Hardly could be fuel than because in the 60's when I started driving and working on motors, fuel at the pump had a nominal octane rating of 100/101 for regular and was leaded with no alcohol added. I don't believe ethenol has anything to do with it. I remember hearing my grandfather talk about vapor lock and it made him angry. I believe the reason for the anger was, the car right next to him DIDN'T have it and he didn't know how to prevent it, embarrassment. I guess this is like the exploding fan, it can't happen, till it happens to you.
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Old 05-30-2012, 07:33 AM   #44
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Default Re: Vapor lock!

You can call it what you like, but my 28 coupe does not run good after it sits and is restarted in hot weather. I have put a phenolic spacer between carb and manifold. Also rapped the gas line and fuel bowl. This has made a big difference. It never did this until the crap gas came out. In my case I think the manifold heater puts a lot more heat in the engine compartment. But it has been on the car since it was new in Mich. Also it feels real good in the winter time. So if it is not vapor lock, it is caused from the heat, and poor gas.
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Old 05-30-2012, 07:54 AM   #45
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Default Re: Vapor lock!

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Originally Posted by steve s View Post
I have seen vapor lock in a Model A with my own eyes. I watched, repeatedly, as clear plastic inline filter filled up with vapor and stalled the motor. I've posted photos (seen in a link provided earlier) of vaporization occuring in the sediment bowl--amazingly, large bubbles of vapor could be seen to pass through the system with barely a hiccup. So, there is absolutely no doubt (in my mind) that fuel vaporization can occur in the A fuel path, and that it may or may not kill the motor.
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Originally Posted by Mountain Dew View Post
Why did the vapor stop at the filter? Why didn't the vapor pass through the fuel line and vent through the gas tank?
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Originally Posted by BILL WILLIAMSON View Post
The pressure of the column of gas above the filter had it blocked, like you can't burp while rapidly chugging water!
I would like more explanation along these lines above.

I have the same confusion... Since fuel is heavier than vapor, it should flow downward while vapor bubbles upward. The vapor should eventually make it's way back to the gas tank. The "pressure" explanation above doesn't seem likely. Why wouldn't the fuel continue to flow down past the vapor? Gravity is the only factor at play here, right?
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Old 05-30-2012, 08:16 AM   #46
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Originally Posted by newshirt View Post
I would like more explanation along these lines above.

I have the same confusion... Since fuel is heavier than vapor, it should flow downward while vapor bubbles upward. The vapor should eventually make it's way back to the gas tank. The "pressure" explanation above doesn't seem likely. Why wouldn't the fuel continue to flow down past the vapor? Gravity is the only factor at play here, right?

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You can call it what you like, but my 28 coupe does not run good after it sits and is restarted in hot weather. I have put a phenolic spacer between carb and manifold. Also rapped the gas line and fuel bowl. This has made a big difference. It never did this until the crap gas came out. In my case I think the manifold heater puts a lot more heat in the engine compartment. But it has been on the car since it was new in Mich. Also it feels real good in the winter time. So if it is not vapor lock, it is caused from the heat, and poor gas.

Ok I am, ...and have been in the same mindset. To me, this is why we always get into these discussions yet there is never any resolve. Can someone not explain EXACTLY what is happening to cause this? In other words, exactly what is the heat doing, ...or what exactly is happening with the poor gas that is causing this? I would like to understand more than just someone saying "it turns into a vapor."

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Old 05-30-2012, 09:45 AM   #47
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Default Re: Vapor lock!

Quote:
Originally Posted by Mountain Dew View Post
.

Why did the vapor stop at the filter? Why didn't the vapor pass through the fuel line and vent through the gas tank?
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Originally Posted by BILL WILLIAMSON View Post
The pressure of the column of gas above the filter had it blocked, like you can't burp while rapidly chugging water! Bill W.
I think Bill answered it. My only quibble would be with the word "rapidly"; if there were rapid fuel flow holding the bubble down, there would be no problem. In reality, the fuel flow around a bubble might or might not be enough flow to allow the car to sputter along.


Quote:
Originally Posted by BRENT in 10-uh-C View Post
Steve & Gary, ...using your scenario of vaporization in the fuel line, please explain exactly what is happening in your view? I understand the air pocket in-between two liquids, but what is happening when the lower level of fuel in the fuel line depletes? A Model-A carburetor will still perform with a bowl half-full, and as soon as the float drops pulling the needle down, you really shouldn't have any more backpressure to hold the "air bubble" (vapor) in the line. (Remember the bowl is vented where it cannot hold pressure.) So again, would somone please explain in minute details exactly what is happening from the beginning until the end as to why this is called 'vapor lock'?

As far as not believing that percolated fuel can be sticky, all I can say is try it like I did several years ago. Pour a little gas in a bowl off of a Zenith carburetor and warm the bowl. I used a very small flame but you do whatever you feel comfortable with. Just waving the heat under the bowl will cause the carburetor bowl to become extremely warm all over. I just got it hot enough that the fuel simmered and evaporated. It doesn't take long for the fuel to disappear ,and as it was cooling down I stuck my finger in the bowl and the floor of the bowl was sticky. Again, for those that don't subscribe to my theory, then so be it.
Maybe a less graphic example than Bill's would help folks accept the fact gravity doesn't always win. Surely, we've all experienced a sink being blocked by an air bubble "trapped" under an "open" stopper; it won't drain until the stopper is jiggled around to let the air burp out. That is a gravity flow system, with liquid above a bubble, and an open vent below the bubble--sound familiar? It happens, guys.

If you want a more scientific explanation, I think it has to do with surface tension of bubbles. Before a big bubble, like that under a drain plug in an inline filter, can either squeeze by the plug or up a skinny fuel line, it has to undergo an energetically unfavorable decrease in radius of curvature. I'm not saying I totally buy it, but if someone needs a theory before they can believe their eyes, there you go.

Regarding your percolation theory, I don't doubt that a bit of sticky stuff will be left when gasoline evaporates. The part I don't understand is how that sticky stuff gets up on the shut-off valve when the evaporating puddle must be primarily down in the bottom of the bowl.

Semantics: This isn't important but I don't underdstand use of the term "percolation" to describe boiling off the fuel in a carb bowl; as I understand it, it's not much like what goes on either in a percolator coffee pot or in a septic bed perc test. I realize that our use the term "vapor lock" to refer to any issues deriving from unwanted fuel vaporization (including percolation) also can be criticized.

Earlier you asked how riding the choke could possibly help a vapor lock situation. My guess is that it simply takes what meager fuel is available and adjusts the air/fuel mix ratio to something more useable. Clearly, as you say, if there were complete "lock" of fuel flow, it wouldn't help, at least not for very long.

So many threads--so little time.

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Old 05-30-2012, 10:07 AM   #48
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Default Re: Vapor lock!

It's short notice, but since the MARC meeting is in Oshkosh next month, why not invite a guest speaker to shed some light on the subject? Someone local with extensive experience in thermodynamics and heat transfer would be ideal....someone who knows the difference between vapor and gas. Two potential candidates would be Richard Goldstein and Ephraim Sparrow from the University of Minnesota. Both of these guys are experts in heat transfer and thermodynamics with a lifetime of theoretical, scientific, and practical experience.

I don't have any experience with vapor lock...but get tired of all the bloviating. Just do whatever it takes to get your vehicle running.
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Old 05-30-2012, 10:47 AM   #49
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Default Re: Vapor lock!

Walt had the same EXACT EXACT on the money problem as you.. Here is what WE did to correct it..
Drained the gas tank and filtered the gas, seems many time and it was a problem with an old cork that was flaking and blocking the fuel
CLEANED thoroughly the carb and all the jets, removed and cleaned all of them, cleaned fuel bowl and added NEW Filter
FINALLY. Changed the Gas cap to one that is vented properly
NEVER EVER had a problem since

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Old 05-30-2012, 11:36 AM   #50
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Default Re: Vapor lock!

Here's another thought:

For those of you going to Oshkosh, you might have an opportinuty to learn about vapor formation and fuel delivery. Since the meeting is at the EAA grounds, look around and see if there are any exhibits/posters that metion vapor formation, deviation from ideal air:fuel ratio, oxygenation, altitude, or whatever dealing with reliable fuel delivery and combustion. Aircraft engineers and pilots have experience with this topic.
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Old 05-30-2012, 02:06 PM   #51
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Default Re: Vapor lock!

I wonder if these fuel problems happen more often on cars with cast iron or glass sediment bowls??? There's probably a reasonably common cause, if we can discover it. One poster has 2 cars that never do it & 1 car that DOES it. All 3 cars have common stock equipment. Bill W.
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Old 05-30-2012, 02:24 PM   #52
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Default Re: Vapor lock!

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Originally Posted by BRENT in 10-uh-C View Post
The other thought I ponder is folks are basing this issue now on the ethenol laced fuels. Back a few decades ago when vapor lock was an issue, what was the blame then? Ethenol fuel??
An excellent point and your common sense/historical perspective trumps the thoughts of these folks. The volativity of a liquid is the factor, and ethanol added to gasoline lowers the volativity. In other words, ethanol makes engines run less efficiently but lowers the occurence of vaporization of the fuel.
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Old 05-30-2012, 02:53 PM   #53
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Default Re: Vapor lock!

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Originally Posted by newshirt View Post
I would like more explanation along these lines above.

I have the same confusion... Since fuel is heavier than vapor, it should flow downward while vapor bubbles upward. The vapor should eventually make it's way back to the gas tank. The "pressure" explanation above doesn't seem likely. Why wouldn't the fuel continue to flow down past the vapor? Gravity is the only factor at play here, right?
Likewise, since water is heavier than air why can I suspend a drop of water on my fingertip and it doesn't fall? Gravity is not the only factor here but just a part. Surface tension and cohesion with a touch of adhesion all play a part to counteract gravity.

Hyperphysics - Georgia State University

"The cohesive forces between molecules down into a liquid are shared with all neighboring atoms. Those on the surface have no neighboring atoms above, and exhibit stronger attractive forces upon their nearest neighbors on the surface. This enhancement of the intermolecular attractive forces at the surface is called surface tension."


"Molecules liquid state experience strong intermolecular attractive forces. When those forces are between like molecules, they are referred to as cohesive forces. For example, the molecules of a water droplet are held together by cohesive forces, and the especially strong cohesive forces at the surface constitute surface tension.


When the attractive forces are between unlike molecules, they are said to be adhesive forces. The adhesive forces between water molecules and the walls of a glass tube are stronger than the cohesive forces lead to an upward turning meniscus at the walls of the vessel and contribute to capillary action."

Hope this helps.
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Old 05-30-2012, 03:15 PM   #54
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Originally Posted by steve s View Post
I think Bill answered it. My only quibble would be with the word "rapidly"; if there were rapid fuel flow holding the bubble down, there would be no problem. In reality, the fuel flow around a bubble might or might not be enough flow to allow the car to sputter along.




Maybe a less graphic example than Bill's would help folks accept the fact gravity doesn't always win. Surely, we've all experienced a sink being blocked by an air bubble "trapped" under an "open" stopper; it won't drain until the stopper is jiggled around to let the air burp out. That is a gravity flow system, with liquid above a bubble, and an open vent below the bubble--sound familiar? It happens, guys.
Steve
I'm confused by Steve's "air trapped under an open stopper" analogy. Is this describing vapor lock or trash in a fuel line?

Bill W.'s comparing the fuel line with a human esophagus is off the mark. Our beloved Model A's are not living organisms.

Simple question, what would keep a vapor bubble from passing up through the fuel line and venting through the gas tank? Perhaps a high spot in the fuel line ,trash in the line, bad fuel cap, something like that.
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Old 05-30-2012, 03:25 PM   #55
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Originally Posted by BRENT in 10-uh-C View Post
Ok I am, ...and have been in the same mindset. To me, this is why we always get into these discussions yet there is never any resolve. Can someone not explain EXACTLY what is happening to cause this? In other words, exactly what is the heat doing, ...or what exactly is happening with the poor gas that is causing this? I would like to understand more than just someone saying "it turns into a vapor."

.
This could be a new bumper sticker "VAPOR HAPPENS". When the molecules of a liquid are heated the bonds between them break and a liquid becomes a gas, i.e. water converts to steam. This molecular breakdown will continue until the liquid is "boiled" away, the heat is removed or the liquid/gas reach equilibrium.

Hyperphysics - Georgia State University

"The process of evaporation in a closed container will proceed until there are as many molecules returning to the liquid as there are escaping. At this point the vapor is said to be saturated, and the pressure of that vapor (usually expressed in mmHg) is called the saturated vapor pressure.

Since the molecular kinetic energy is greater at higher temperature, more molecules can escape the surface and the saturated vapor pressure is correspondingly higher. If the liquid is open to the air, then the vapor pressure is seen as a partial pressure along with the other constituents of the air. The temperature at which the vapor pressure is equal to the atmospheric pressure is called the boiling point."

Now that we have vaporized fuel in a closed space, tension, cohesion and adhesion take over to finish the drama as explained in my previous post for newshirt.

This may/probably doesn't meet your EXACT standards but it is the best this physics lovin, chemistry dropout can do. Like I mentioned before, I didn't believe a gravity system could vapor lock.
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Old 05-30-2012, 03:30 PM   #56
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Simple question, what would keep a vapor bubble from passing up through the fuel line and venting through the gas tank?
Surface tension and adhesion.
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Old 05-30-2012, 08:09 PM   #57
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Default Re: Vapor lock!

I had this happen quite a bit last summer 105 out if i was at a red light to long it would vaper lock i just unscrew the drain plug let it flow fr one sec and cool carb as soon as temp outside drops a bit ie from day time to night the problem goes away up in ossipee NH you could still get real gass if i used real gass no problem rember alcohal boils at 160 degrees very posible for the temp under the hood to reach 160 very easey on hot day then all the alcohal in the line boils and causes vaper lock
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Old 05-31-2012, 09:01 AM   #58
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Default Re: Vapor lock!

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Originally Posted by Mountain Dew View Post
I'm confused by Steve's "air trapped under an open stopper" analogy. Is this describing vapor lock or trash in a fuel line?

Bill W.'s comparing the fuel line with a human esophagus is off the mark. Our beloved Model A's are not living organisms.

Simple question, what would keep a vapor bubble from passing up through the fuel line and venting through the gas tank? Perhaps a high spot in the fuel line ,trash in the line, bad fuel cap, something like that.
Sorry for the confusion. I was talking about a sink with a stopper that is raised and lowered by a hinged push rod arrangement--not a completely removable stopper or a plugged drain line. When the rod is pulled up, the stopper drops; when the rod is pushed down, the stopper lifts a bit and water can drain around it. In my experience, which I may have mistakenly assumed to be universal, sometimes the sink still won't drain even with the stopper in the open position. When it is jiggled around, a bubble of air burps out and draining commences.

Technically, this is not vapor lock since the bubble is air, not vapor. But otherwise it is a good example of how a bubble can block gravity driven flow of liquid even when the system is open to the atmosphere above and below. Such a bubble can form in an inline fuel filter, which is what the original question was about.

I believe that the basic explanation for the blockage in the face of gravity is surface tension.

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Old 05-31-2012, 09:06 AM   #59
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Originally Posted by 1928Pickuppain View Post
I had this happen quite a bit last summer 105 out if i was at a red light to long it would vaper lock i just unscrew the drain plug let it flow fr one sec and cool carb as soon as temp outside drops a bit ie from day time to night the problem goes away up in ossipee NH you could still get real gass if i used real gass no problem rember alcohal boils at 160 degrees very posible for the temp under the hood to reach 160 very easey on hot day then all the alcohal in the line boils and causes vaper lock
The problem is not the boiling point of alcohol; gasoline actually starts to boil around 100 F. Others have pointed out that vapor lock doesn't happen in cars that run on pure alcohol. The problem is the more subtle effect of the presence of alcohol actually making the gasoline molecules want to evaporate even more readily.

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Old 05-31-2012, 01:48 PM   #60
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In my experience, which I may have mistakenly assumed to be universal, sometimes the sink still won't drain even with the stopper in the open position.
Steve
Steve,
This is a prime example of surface tension, however, in this example the root cause of the trapped air bubble is usually a non-operational vent pipe. If the drain is properly vented the vents can sometimes accumulate leaves in the pipe and cease to work properly.
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