Vapor lock!

[kingbee]

My first drive in an A in HOT weather in 40 years. (and back then we had good gas) After an hours drive, shut down the engine for a few minutes and it would not restart. Lots of cranking proved frutile. Held the choke out for 20 strokes, nothing, INCLUDING not even a drop of fuel from the carb. Checked the spark & it was strong. 40 minutes later it started. 30 minutes later it died at a stop - same scenario.

My question is not If I had vapor lock, since the spark was good. I searched out all the threads on the barn, and there were mentions of Marvel mystery Oil (among other things) being added to the fuel.

Finally my question - how much should be added per gallon to help eliminate the problem?

[BILL WILLIAMSON]

Read the fuel starvation thread----Bill W.

[James Rogers]

If vapor lock exists, can someone here convince me why my T has never exhibited any signs of it? This T has been driven in 105 degree weather, has no water pump and is gravity feed with the carburetor right next to the exhaust. I use the same gas as everyone else whether it has corn in it or not. It never fails to start no matter the temperature and is hand crank only.

[steve s]

Take heart, kingbee, because some people have not experienced vapor lock, it can't possibly be happening to you!

[John Duden]

i took My 1951 john deere G on a tractor ride yesterday for our tractor club, i made it 20 out of 25 miles until it vapor locked. I let it cool down and put in a couple of table spoons of water in the gas tank and let it idle, when it quit, ( water went into the carb) i cranked it over with the key off for about 5 seconds, it then started right up and never had a problem again. When the water went throught the carburator, it cooled it since it has a higher boiling point and and would not burn, when it was flushed out of the carb and into the manifold it cooled the pistons and valves,
Worked for me, I have since added some oil in the tank.
add about a half a cup for 10 gallons, i ran a cup in 20 gallons
John

[Patrick L.]

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There seems to be many cures for vapor lock from clothes pins to MMO.. A little kerosene or diesel fuel mixed well with the gas even helps.. But, with fuel prices today the MMO may be cheaper.. Personally I think a heat shield around the exhaust pipe seems to work best..

[Ken B]

I have experienced this with my 30 Coupe. The problem turned out to be a gas cap that didn't vent properly. On one trip, it started backfiring and quit. After all the common checks, I went to open the gas cap and heard a vacuum sound. It is a reproduction gas cap and it wasn't venting properly. The old original one worked great.

[Mike]

I would try a new GOOD condenser. worked for me

mike

[kingbee]

Ken, thanks for your suggestion - I checked that, as it's a common problem on the Honda Valkyrie.

Thanks Mike, but I had a good strong spark which I tested, as I knew it could be a possibility...

[steve s]

Originally Posted by James Rogers

If vapor lock exists, can someone here convince me why my T has never exhibited any signs of it? This T has been driven in 105 degree weather, has no water pump and is gravity feed with the carburetor right next to the exhaust. I use the same gas as everyone else whether it has corn in it or not. It never fails to start no matter the temperature and is hand crank only.

James,

I appreciate your puzzlement. All I can say is that this is kind of a spooky issue. The oddest case I know of is a fellow in our club (Dan/Kzo) who has two A's that NEVER vapor lock and one that ALWAYS does (temps >90 F). Same carbs, engine pans, distributors, gasoline, driving habits, weather, altitude, etc. His story is the 8th one down in this earlier vapor lock thread:

http://www.fordbarn.com/forum/showth...ock#post214082

Steve

[Patrick L.]

I think I understand what Kingbee is referring to.. The Valkyrie doesn't really have a vapor lock issue,, but,, it does have a fuel starvation problem when the fuel tank has been removed and its then easy to pinch the fuel tank vent line and not notice it.. So, I think we are talking about the same thing..

[H. L. Chauvin]

Hi Kingbee,

Four (4) ounces of Marvel Mystery Oil to 10 gallons of gasoline will work in answering your final, single question:

"Finally my question - how much should be added per gallon to help eliminate the problem?"

[BrianBurkert]

If you don't have MMO or diesel at your disposal, shutting the gas valve and running the carburetor dry at a pit stop helps. When you go to leave, open the valve and the carb will refill with cool gasoline from the tank.

[Tom Wesenberg]

Originally Posted by BrianBurkert

If you don't have MMO or diesel at your disposal, shutting the gas valve and running the carburetor dry at a pit stop helps. When you go to leave, open the valve and the carb will refill with cool gasoline from the tank.

A few years ago I was parked in the hot parking lot of the Twin Cities Ford plant and had ethanol laced crap gas in my tank. I went to start the car after being parked for a few hours and found the gas had boiled the carb dry. When I opened the valve the gas wouldn't start flowing until I opened the fuel line at the carb. When I made another stop that same day for another few hours the exact same thing happened again. Never had that happen with the good gas I've been buying lately.

[marc hildebrant]

But Tom, it hasn't happened to some people, so it can't be true !



Marc

[James Rogers]

Originally Posted by steve s

James,

I appreciate your puzzlement. All I can say is that this is kind of a spooky issue. The oddest case I know of is a fellow in our club (Dan/Kzo) who has two A's that NEVER vapor lock and one that ALWAYS does (temps >90 F). Same carbs, engine pans, distributors, gasoline, driving habits, weather, altitude, etc. His story is the 8th one down in this earlier vapor lock thread:

http://www.fordbarn.com/forum/showth...ock#post214082

Steve

Steve, I also watched Brent remove not only the fan from his T but the bottom pulley on the same day in the same heat in Minnesota no less. I thought he was nuts and would destroy a motor I had just reconditioned with a Stipe cam and a Scat crank. The car ran great and had no overheating or vapor lock problems. I don't believe in vapor lock because of situations like this. We were using gas with corn in it right from any convenient pump. I don't believe alcohol gives any problems other than the BTU's are lower. This means with lower BTU's engines would run at lower temps.

[marc hildebrant]

J. Rodgers

So, what reason are you giving for the engine to run rough on hot day's ?

In my case, the engine ran real rough with very little power until I pulled out the choke some. After awhile it ran O.K.

Only happened on real hot days under the conditions I have talked about

If not vapor lock, then what ?

Surely you do not think that because it hasn't hapened to you, then it can't be true.


Marc

[jkeesey]

On the original post I believe your float valve may have stuck. Mine has done the exact same thing before. I personally don't believe in vapor lock not because it has never happened to me but because it is a term thrown around simply when someone doesn't know the problem. The alchohol in fuel boils at around 170 degrees and gasoline boils around 200. I've never seen a car when I cannot lay my hand on the carburetor because it is that hot.

[James Rogers]

Originally Posted by marc hildebrant

J. Rodgers

So, what reason are you giving for the engine to run rough on hot day's ?

In my case, the engine ran real rough with very little power until I pulled out the choke some. After awhile it ran O.K.

Only happened on real hot days under the conditions I have talked about

If not vapor lock, then what ?

Surely you do not think that because it hasn't hapened to you, then it can't be true.


Marc

I am a realist, if I see it I might believe it. There are many things heat can affect that will keep a motor from running. Could be a bad condenser, a weak coil, the starter could be pulling too many amps and robbing the distributor, I have even seen the fuel tank expand enough to touch the wires on the ignition switch and short them out till the tank was at half full or the cap was loosened to let out the pressure. When a car sits for a short time after running without the fan to push heat out of confined spaces accumulated heat will affect lots of electrical parts. I don't believe in vapor lock, jkeesey is right, it is easier and sounds better to say vapor lock than "I don't know".

[BRENT in 10-uh-C]

Lets go another direction. Think about a riding lawn tractor that we mow the grass with. Everyone is generally using the same "ethanol-laced" fuel in those as we do in our automobiles. The underhood heat those generate is extreme because there is little airflow under the hood and the engine is laboring mightily during the mowing process. Why does this "vapor lock phenomenon" not seem to affect these machines?

[Hicktick]

Well back in the day mama had a 56 chevy wagon and on a trip to the Smokey mtns. , she started running ruff .
After a good climb she quit and we coasted down hill to a pulling off spot with picknic tables.
My father took the breather off and climbed on top if the engine and said its vapor locked.
I had no idea what that was but hoped we might have to spend the nite.
While they prepared our lunch dad and I walked down to a store and he got a big bag of ice.
He piled that ice on the intake and my first thought was that will crack something.
After we ate and rested all the ice melted , she started up and ran fine all the way home , as traffic had cleared and you could get up some speed .
Later in life I saw it many times at the drag strip.

[Farrell In Vancouver]

I have a question. Are the bowls not vented to atmosphere in order for the gravity feed to work? Head pressure is all great until it cannot displace what is in the bowl, such a high pressure vaporized fuel? I cannot see how this would work without a vent to atmosphere, and most carburettors I have seen, have a vent some where in order to push fuel through the various circuits and jets. (Vacuum asissting) Some folks are saying the cracking the line to the carb will relieve this problem.
Is it beacause of a full, or partial oclusion of the vent port?
Same with the tank. If air cannot enter, it will not let the fuel out.
Just asking, as I have never experienced "Vapor lock" and wouldn't know it if I saw it.

[BRENT in 10-uh-C]

The one other thing that intrigues me is these folks who pull the choke out to cure the 'vapor locking' problem. In your opinion, what is happening during that little exercise that corrects the problem?


I have studied the operation of a Zenith carburetor and personally I cannot understand how this would help. The vacuum that is being created through the venturi will pull harder on the jet however as soon as the bowl is dry of fuel, the extra burst of vacuum is for naught as it cannot pull a vacuum up into the bowl and then into the float needle & seat, and then into the fuel line to get the flow flowing again. So "what" does the choke do to help?

Again, my thoughts are, if there is fuel in the bowl it is indeed possible it will draw more fuel through the jet and richen up the mixture, HOWEVER if fuel is present and being replenished, then that can't be "vapor lock". If there is vapor in the bowl, pulling the choke will not richen the mixture of vapor. Again, I have stated this over & over here but I believe it is fuel percolation in the bowl that boils the fuel and when it evaporates, the fuel dries leaving a sticky residue that tends to clog passages and create a sticky float valve which is causing the problems. Once fuel is able to flow past those objects, the cleansing agents in the gasoline will remove the deposits and things return to normal. IMO, "vapor lock" and percolation are not the same.

[Jerry Parr WI]

I have one car that exibits the problem and one that does not. Try the following solutions to verify the problem. If you do not have an indented firewall cool the gas by keeping the sediment bowl in ice. A can in an insulated holder works short term. Permanent solution is fuel pressure. My problem car has a fuel pump and turning it on makes the spiting and back firing stop almost instantly. Many claim the problem is electrical but if fuel pressure cures the electrical problem so be it.

Prior to the gas shortages in the late 70's this car had no problems at temperatures well over 100 deg. As the volatility of gas has increased to get more yield from a gallon of oil and to compensate for the octane loss without lead the problem increases.

[Patrick L.]

I think the two terms are used interchangeably .. I would think that fuel perk is generically called vapor lock.. Not to be a PITA but I guess I've thought that perk caused vapor lock,, but,, I haven't thought about it much..

[steve s]

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Originally Posted by Farrell In Vancouver

I have a question. Are the bowls not vented to atmosphere in order for the gravity feed to work? Head pressure is all great until it cannot displace what is in the bowl, such a high pressure vaporized fuel? I cannot see how this would work without a vent to atmosphere, and most carburettors I have seen, have a vent some where in order to push fuel through the various circuits and jets. (Vacuum asissting) Some folks are saying the cracking the line to the carb will relieve this problem.
Is it beacause of a full, or partial oclusion of the vent port?
Same with the tank. If air cannot enter, it will not let the fuel out.
Just asking, as I have never experienced "Vapor lock" and wouldn't know it if I saw it.

Yes, the bowls are vented to the atmosphere. The handiest picture I have is of a B carb showing where the vent was plugged to adapt it to an air filter.



I understand your question and have no answer. I agree that it doesn't make sense that cracking the feed line to a vented chamber could work--but I believe the people who say that it does. Brent's idea that percolation (why not call it vaporization?) in the bowl could so quickly gum up the float valve sounds far fetched to me, but I've got nothing better.

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.

Steve

[Mountain Dew]

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

.

Why did the vapor stop at the filter? Why didn't the vapor pass through the fuel line and vent through the gas tank?

[BRENT in 10-uh-C]

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.

[jkeesey]

I'm with ya Brent. I could easily see this "stickyness" occuring and sticking a float valve shut. I've delt with fuel evaporating and cooking out of carbs on old motorcycles all the time. The fuel being cooked out of the bowl is not the hard part to deal with its what's left behind.

[BRENT in 10-uh-C]

And for all the other naysayers, the other way to look at all of this is just to remember the motto by which many Model-A restorers live by;

If it can't be fixed with a hammer, ...then it's an electrical problem!!

.

[Milton]

I found the first sentence from the following excerpt surprising because I really doubted it. Anyway I hope this information is helpful.

From Wikipedia:
Gravity feed fuel systems are not immune to vapor lock. Much of the foregoing applies equally to a gravity feed system; if vapor forms in the fuel line, its lower density reduces the pressure developed by the weight of the fuel. This pressure is what normally moves fuel from the tank to the carburetor, so fuel supply will be disrupted until the vapor is removed, either by the remaining fuel pressure forcing it into the float bowl and out the vent or by allowing the vapor to cool and re-condense.

Vapor lock is also less common in other motor sports, such as Formula One and IndyCar racing, due to the use of fuel injection and alcohol fuels (ethanol or methanol), which have a lower vapor pressure than gasoline.

[Duffy1]

I also have this problem .I put this on the other thread but will also post it here . A fellow model a`r who is a second generation model a`r has a theroy that the Zenith carburator with the cast iron housing acts as a heat sink and when you stop the engine and let the engine sit for a while the heat from the carburator turns the gas to vapor and then when you are ready to go the engine will start but soon dies out . Pulling out the choke will keep the car going ,alibet not to good , until fresh gasoline gets into the carb . He changed to a carb that does not have a cast iron housing .

[jkeesey]

I'm not going to argue the point farther but if anyone on here didn't know anybody can edit or post on Wikipedia.

[James Rogers]

Originally Posted by Milton

I found the first sentence from the following excerpt surprising because I really doubted it. Anyway I hope this information is helpful.

From Wikipedia:
Gravity feed fuel systems are not immune to vapor lock. Much of the foregoing applies equally to a gravity feed system; if vapor forms in the fuel line, its lower density reduces the pressure developed by the weight of the fuel. This pressure is what normally moves fuel from the tank to the carburetor, so fuel supply will be disrupted until the vapor is removed, either by the remaining fuel pressure forcing it into the float bowl and out the vent or by allowing the vapor to cool and re-condense.

Vapor lock is also less common in other motor sports, such as Formula One and IndyCar racing, due to the use of fuel injection and alcohol fuels (ethanol or methanol), which have a lower vapor pressure than gasoline.

If this is true then, why does this happen in systems like Ford flathead 8's and late chevy 6's and 8's with fuel pumps? Also why does it not happen in modern cars? Wives tale because the person it's happening to has no better explanation.

[1931 flamingo]

There has been an extensive post by G.M. on the EV8board about v/lock along with temp cks etc. Interesting. Possible solution to this problem would be to add an elec in-line f/pump on the A.
Paul in CT

[BILL WILLIAMSON]

Originally Posted by James Rogers

If this is true then, why does this happen in systems like Ford flathead 8's and late chevy 6's and 8's? Also why does it not happen in modern cars? Wives tale because the person it's happening to has no better explanation.

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.

[Milton]

I really felt this would occur.

jkeesey,
Another source, Webster's Online Dictionary, unlike Wikipedia Webster's isn't open to public editing:

"Do not assume that a gravity feed fuel system is immune to vapor lock simply because there is no fuel pump to "upset”. Much of the foregoing applies equally to a gravity feed system. Vapor lock has been the cause of many a forced landing in aircraft. That is why aviation fuel (AVGAS) is manufactured to far higher vapor pressure than automotive gasoline (petrol). In addition aircraft are far more susceptible because of their ability to change altitude rapidly. Liquids boil at lower temperatures when in lower pressure environments."

James,
Pardon the delay dinner time on the left coast.
"If this is true then, why does this happen in systems like Ford flathead 8's and late chevy 6's and 8's?"

Negative fuel pressure at the pump inlet. Low pressure pumps. Pump higher than fuel level.

"Also why does it not happen in modern cars?"

Fuel pumps are in the gas tank (cool) and have very high pressures relative to the pre 80's vehicles.

[BILL WILLIAMSON]

Originally Posted by Mountain Dew

.

Why did the vapor stop at the filter? Why didn't the vapor pass through the fuel line and vent through the gas tank?

The pressure of the column of gas above the filter had it blocked, like you can't burp while rapidly chugging water! Bill W.

[Duffy1]

Next time I drive my car and I am going to let the car sit for more than 5 minutes I am going to do as one post suggested . Close the fuel valve and run all the gas out of the carburator.

[caserider]

interesting article...not specifically about Ford, but worth a glance. Mentions vapor lock on the last page:

http://everythingengines.files.wordp...el-article.pdf

[BRENT in 10-uh-C]

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??

[James Rogers]

Originally Posted by BILL WILLIAMSON

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 .

[James Rogers]

Originally Posted by BRENT in 10-uh-C

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.

[George Miller]

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.

[newshirt]

Originally Posted by steve s

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.

Originally Posted by Mountain Dew

Why did the vapor stop at the filter? Why didn't the vapor pass through the fuel line and vent through the gas tank?

Originally Posted by BILL WILLIAMSON

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?

[BRENT in 10-uh-C]

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Originally Posted by newshirt

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?

Originally Posted by George Miller

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."

.

[steve s]

Originally Posted by Mountain Dew

.

Why did the vapor stop at the filter? Why didn't the vapor pass through the fuel line and vent through the gas tank?

Originally Posted by BILL WILLIAMSON

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.

Originally Posted by BRENT in 10-uh-C

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.

Steve

[caserider]

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.

[msmaron]

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

Mark'

[caserider]

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.

[BILL WILLIAMSON]

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.

[Milton]

Originally Posted by BRENT in 10-uh-C

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.

[Milton]

Originally Posted by newshirt

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.

[Mountain Dew]

Originally Posted by steve s

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.

[Milton]

Originally Posted by BRENT in 10-uh-C

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.

[Milton]

Originally Posted by Mountain Dew

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.

[1928Pickuppain]

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

[steve s]

Originally Posted by Mountain Dew

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.

Steve

[steve s]

Originally Posted by 1928Pickuppain

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.

Steve

[Milton]

Originally Posted by steve s

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.

[steve s]

Originally Posted by Milton

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.

Milton,

I know what you're saying, but in the case I deal with daily, it's a fairly new, well vented, construction. The problem is that a decorative covering on the stopper narrows the drainage gap just a tad. The plumber pointed out to me what was going to happen when he did the installation. He demonstrated the flow difference with and without the cover. Maybe an issue with Delta. Sounds a bit off-topic but I still think it's great example of the point I was trying to make.

Steve

[Milton]

Steve,
I certainly agree with you about the example. I have yet to hear from BRENT in 10-uh-C but, other than that, I feel comportable with our findings here and figure that, unlike Float A Motors and oil, we just might have put this topic to sleep.

[BILL WILLIAMSON]

Wherever or whatever is causing these problems, to me, seems to be related to underhood temps. I wonder if it is either more or less prevalent with different fan configurations??? Studying the carb top filter chamber, I strongly believe that boiling gas in there can't escape through the needle & seat & backs up into the gas line causing no fuel flow. If this could be he root cause, the next challenge would be to keep that chamber area cooler.
Before OSHA & all these GREEN PEOPLE, Ol'Bill might have imagined, "If someone makes a self adhering asbestos putty-like goop, I'll layer it on that area to keep it cool & paint it flat black!" Wish I could talk to Chief, I'll bet you this is not just a "modern day" problem!! Bill W.

[Tom Wesenberg]

Originally Posted by BILL WILLIAMSON

Wherever or whatever is causing these problems, to me, seems to be related to underhood temps. I wonder if it is either more or less prevalent with different fan configurations??? Studying the carb top filter chamber, I strongly believe that boiling gas in there can't escape through the needle & seat & backs up into the gas line causing no fuel flow. If this could be he root cause, the next challenge would be to keep that chamber area cooler.
Before OSHA & all these GREEN PEOPLE, Ol'Bill might have imagined, "If someone makes a self adhering asbestos putty-like goop, I'll layer it on that area to keep it cool & paint it flat black!" Wish I could talk to Chief, I'll bet you this is not just a "modern day" problem!! Bill W.

Why paint it black?
When you want to radiate the heat AWAY from an INTERNAL source, such as a motorcycle cylinder, then flat black works best.

When you want to reflect heat away from an external source, such as the Model A exhaust manifold, white works best. That's why I was lucky to find a white plastic covering that fit over my fuel line when I was using the crap gas. With good gas, I removed the cover and keep it under the rear seat.

[BILL WILLIAMSON]

Originally Posted by Tom Wesenberg

Why paint it black?
When you want to radiate the heat AWAY from an INTERNAL source, such as a motorcycle cylinder, then flat black works best.

When you want to reflect heat away from an external source, such as the Model A exhaust manifold, white works best. That's why I was lucky to find a white plastic covering that fit over my fuel line when I was using the crap gas. With good gas, I removed the cover and keep it under the rear seat.

The black was for asthetics & Fine Points Judging.
Tom, Your comment about my reputation was the nicest thing anyone could have said to me today, even surpassing Gregg saying, "Hey,Dad, got your Burgundy Wine, you forgot to put it on your list!"
Bill W.

[Blessyouboys]

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Originally Posted by BILL WILLIAMSON

Before OSHA & all these GREEN PEOPLE, Ol'Bill might have imagined, "If someone makes a self adhering asbestos putty-like goop, I'll layer it on that area to keep it cool & paint it flat black!"

What area do you want to cover with putty-like goop?

[steve s]

Originally Posted by BILL WILLIAMSON

...Studying the carb top filter chamber, I strongly believe that boiling gas in there can't escape through the needle & seat & backs up into the gas line causing no fuel flow. If this could be he root cause, the next challenge would be to keep that chamber area cooler. ...

Bill,

I don't know about your black goop, and I've got Cling's radiator fan in my car and believe vapor lock problems occurs with all kinds of fans. However, I bet you have hit on an important factor--a vapor bubble in that screen chamber, with the only ways out thru smaller orifices, is a perfect setup for a metastable bubble blockage. Briefly cracking the gas line fitting could disturb the situation enough to allow gravity to take back over again--probably even cooling things down a bit too, as dribbled gasoline evaporated.

Steve

[Duffy1]

I have not tried it yet ,but an earlier post suggested shutting off the gas valve and run all the gas out of the carburator if you are stopping some where and plan to stay lets say over 30 min which by my expariece is how long it takes for the gas to vaporize in the carburator . When you are ready to leave open the valve fresh cool gas into a cooled down carburator should solve the problem . Next time I am out I am going to try this . I did the choke drill and it worked although it was not fun in a lot of traffic ,but a lot better than dieing out in the traffic .

[Milton]

Now that I am a believer of Model A vapor lock I have to ask why. These cars did not come from the factory with a distributor or carburator heat shield so why the need now? I live inland from San Diego up a three mile 7% grade and in the summer my community is called Hell Cajon, yet I have NEVER experienced a vapor lock in an A. In the thirties these cars were overloaded beyond belief yet made the trip from the dust bowl through the desert to California, how? Methinks there is a cause beyond gasoline, cast iron carbs, etc., retarded timing could do it, lean fuel mixture, what else can cause extreme manifold heat? Anyone?

[BILL WILLIAMSON]

Originally Posted by Blessyouboys

What area do you want to cover with putty-like goop?

That raised area on top of the carb where the screen filter resides. Bill W.

[Tom Wesenberg]

In the "good old days" they didn't have to fight the bad effects of ethanol. My 28 has the fan shroud, original fan, carb, manifolds and 4.2 head and only has problems if the temp is over 80 and if I have 10% ethanol crap gas in it. Then I have to pull the choke some to keep from stalling when I pull away from a red light, as it bucks and snorts it's way down the road for a couple blocks and then cools a bit and runs OK until the next stop. Good gas costs more, but I think it's worth it to not have drivability and storage problems. If I use any ethanol gas in my Honda generator, then after a month I have to remove the carb and clean it out before I can start it.

[BILL WILLIAMSON]

Originally Posted by Milton

Now that I am a believer of Model A vapor lock I have to ask why. These cars did not come from the factory with a distributor or carburator heat shield so why the need now? I live inland from San Diego up a three mile 7% grade and in the summer my community is called Hell Cajon, yet I have NEVER experienced a vapor lock in an A. In the thirties these cars were overloaded beyond belief yet made the trip from the dust bowl through the desert to California, how? Methinks there is a cause beyond gasoline, cast iron carbs, etc., retarded timing could do it, lean fuel mixture, what else can cause extreme manifold heat? Anyone?

Yo, Milton,
Betcha' those folks fried a lot of condensors & boiled a lot of carbs, but didn't have the Internet to tell everyone about it. Love that RPU pic, if that dog was BLACK, that could have been my family headin' for ROUTE 66 to go to CALIFORNEY! What adventures we had! Bill W.

[BILL WILLIAMSON]

Just "thinking," a small hose nipple into carb screen access plug, a small nipple sweated high up on the front of the gas tank and connect them with high quality fuel injection hose. This would give an escape route for air bubbles & vapors to get back to the gas tank. (Your thoughts, please!) Bill W.

[Mike V. Florida]

Wow three different posts on the same subject!

I think the common link is heat.

So, why are some cars having the problem and other not?

If you having the problem the problem or not, do you have engine pans installed,
what is your MPG,
what fan do you use,
water or antifreeze,
what grade gas (Reg premium),
how old is your muffer,
do you use one of those inserts in the manifold to seal the exhaust,
what is your average speed,
"Modern" or stock points?

This might give us some common thing to look at.

I don't have the problem, I have engine pans, 18MPG, water, regular with ethenol, 1980's, yes with the insert, 40-45, stock ign.

[1931 flamingo]

Milton n(post 69) and others: In the 30's the engines were "new", most likely no rust/scale formation in the blocks, radiators only a few years old, and people who understood how to set timing correctly, and speeds probably closer to 30-40 mph, AND no ethanol. I, personally, haven't experienced vapor lock, or any other fuel related problems, inside of carb is spotless, running an old in-line metal cannister filter after the elec fuel shut off (late 31 indent. I JMO
Paul in CT

[BILL WILLIAMSON]

Milton,
Glad you don't have "the problem." I haven't had it either.
Have you thought of stopping at the top of your grade for 15 or 20 minutes with gas on & see if it acts up?
We're doing the 100 mile Sierra Scenic Loop soon & I'm going to do several stops to see if mine acts up. Bill W.

[Milton]

Originally Posted by Tom Wesenberg

In the "good old days" they didn't have to fight the bad effects of ethanol.

If I use any ethanol gas in my Honda generator, then after a month I have to remove the carb and clean it out before I can start it.

Do you think, since ethanol is used as an oxygenizer for fuel, that the additional hydrocarbon burning could be increasing the normal operating temperature of the engine?

I understand the generator fuel problem since ethanol has an affinity for water.

[Milton]

Originally Posted by Mike V. Florida

I don't have the problem, I have engine pans, 18MPG, water, regular with ethenol, 1980's, yes with the insert, 40-45, stock ign.

Nor do I, I do not have engine pans, unkown MPG, two blade aluminum fan, 50% antifreeze, regular with ethenol, new glasspack, headers, 50-55+ hard mph, Mallory pointless ign., 5.5 head.

The item that may be saving me is the electric fuel pump that I have installed. Hmmm

[MAG]

Non-believers should not waste their time reading this post.

I concur with Tom. Post #71
"if the temp is over 80 and if I have 10% ethanol crap gas in it. Then I have to pull the choke some to keep from stalling when I pull away from a red light, as it bucks and snorts it's way down the road for a couple blocks and then cools a bit and runs OK until the next stop. "

I and about a dozen or so members tour year-round in an area approx. 250 miles around Austin. There is no ethanol free gas of any octane available in that area. We see a lot of the "vapor lock" problem.

My thoughts are:
The fuel will percolate in the bowl (glass) when the ambient temp. reaches 80 degrees.
The percolation produces "voids" in the fuel supply to the carb.
The voids follow the path of least resistance and that is the fuel line between the bowl and carb. Weight of the fuel in the tank prevents the void from traveling that direction.
Percolation in the carb. does not cause the engine to run rough unless the bowl is nearly empty because the jets are near the bottom. Empty bowl is due to voids in the supply.

We have implemented every suggestion posted here and some we have come up with on our own. None of them have been a FIX. I will list some here:
Fuel - all octane ratings
Additives - MMO, octane booster, diesel fuel, kerosene, StarTron, Sea Foam, and otherss I may have missed. All with variable mixture ratio.
Electric fuel pump with 2lb psi. on Zenith, Zenith B and Tilly carbs. NO Webbers installed.
Fuel line wrapped with rubber, wrapped with head disipating tape, no wrapping.

Current experimentation consists of:
Venting the fuel bowl with 1/16OD capillary tube up to the top center of the firewall. Causes a significant fuel odor in the cab.
Installed a 5/16" fuel line between the bowl and carb. for volume. Thoughts are that with the additional volume provided by the larger diameter, even with the voids, sufficient fuel will be delivered to the carb to keep the engine running properly.

Due to the nature of this problem it is premature to say we have a fix on it. However, on our last tour (about 200 miles) the car equipped as described had no trouble. A couple other cars did.

[Milton]

Originally Posted by BILL WILLIAMSON

Have you thought of stopping at the top of your grade for 15 or 20 minutes with gas on & see if it acts up?

Nope, it has always been my habit to drive across the hill and cool down. Comes from driving before surge tanks were the norm. I never stop at the top hot but, I will give it a whirl when I get my headers back from being coated.

[Ca. Kid]

This thread is getting awfully technical.
Don't laugh but in Vietnam we had a Ford econoline that liked to vapor lock. A good ole country boy suggested putting clothes pins on the fuel line between the fuel pump and the carburetor, it worked! I have used this simple remedy a few other times with success.

[Kurt in NJ]

I can get a little bit of the dreaded "vapor lock" now ---winter gas, big crack in ex manifold at #2 blowing on carb, the inside of the carb has some crap in it, the bowl has xtra vents--- the gasket--it is torn in 4-5 places(some stick to the top, some to the bottom),all my "tuneup" parts are at least 20 years old, the muffler was part of a buy 5 for 100$ deal in the late 70s, my average speed is whatever the rest of traffic is doing, I have never seen any bubbles in my fuel system ---cast iron bowls don't get bubbles , I run the mixture lean, and use a lot of advance.

One thing I did do -many years ago is to remove the burrs at the ends of the fuel pipe so there was no restriction there

After 45 min of idling, and idle speed parade it sputters a little during the parade, push in the clutch, rev engine a little --perhaps 5 seconds it clears out.

Driving at 50, stop for yard sale, leave idling ---start driving again, sputters for 500 feet,then normal

In NJ the only choice is this ethonal stuff

most likely when I get gas again the problem will go away, no problems last summer once the winter gas was out of the system ---although the manifold crack is larger this year

I have engine pans, am not afraid of the original 2 blade fan--it was nos when I started using it

The 46 I had was another story, it would go fine unless I stopped ---the battery wasn't very good, no chance of cranking through it, I had a routine, vice grips for tank drain plug, small can, fill carb, push car, jump in, pop clutch in 2nd gear, repeat if it didn't suck up a prime---I could go anywhere as long as i didn't stop and expect to restart when the engine was warm

[Mike V. Florida]

I would still love to know why some cars get the problem and a friend a few doors down does not? Why is there that much heat buildup that would cause the problem in the engine compartment in some cars and not in others? Nobody in our club here in Florida has the problem so I can't get first hand data. What is the block temp when it happens? What is the carb temp? What is the water temp? Guess we will never know.

[steve s]

Originally Posted by Mike V. Florida

I would still love to know why some cars get the problem and a friend a few doors down does not? Why is there that much heat buildup that would cause the problem in the engine compartment in some cars and not in others? Nobody in our club here in Florida has the problem so I can't get first hand data. What is the block temp when it happens? What is the carb temp? What is the water temp? Guess we will never know.

Mike,

I agree, but you don't have to go "a few doors down"; one fellow in our club has three A's, all with same ignition, head, engine pans, etc., and run well--same driver, same weather, and same gasoline. Two never vapor lock; one always does on warm days. Swapping carbs did not change anything!! Curiouser and curiouser.

I'm wondering if anyone in Florida has the problem. I'm guessing that you guys who live where there's no doubt it's going to be hot a lot get a less volatile grade of gasoline formulated for you.

Steve

[newshirt]

Originally Posted by steve s

Swapping carbs did not change anything!!

Steve,
What about swapping the fuel line between a car without the problem and the car with it?

I got the feeling from reading these posts that vapor lock (which I've never had, knock on wood) occurs because of rapid expansion of gasses from boiling fuel. Sort of like steam pressure, impeding incoming fuel flow, right? Could that be happening inside the fuel line rather than the carb? I'm wondering if thin fuel lines could cause it.

[steve s]

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Originally Posted by newshirt

Steve,
What about swapping the fuel line between a car without the problem and the car with it?

I got the feeling from reading these posts that vapor lock (which I've never had, knock on wood) occurs because of rapid expansion of gasses from boiling fuel. Sort of like steam pressure, impeding incoming fuel flow, right? Could that be happening inside the fuel line rather than the carb? I'm wondering if thin fuel lines could cause it.

Ray,
The cars belong to a friend in our club. I haven't compared the various fuel lines myself. My own experience regarding the fuel line has been contradictory: Insulating the lines on the two cars I've worked on semed to help. On the other hand, I've watched substantial volumes of vapor bubble burp over out of the sediment bowl and flow all the way down the line with the running motor barely stumble. Here's a photo of a growing vapor bubble in my sediment bowl. After it grew to totally cover the screen, the whole bubble would burp down the fuel line, and then the cycle would repeat.



I posted a series of photos showing the whole process in an earlier thread; it didn't matter.

Steve