For vapor lock nonbelievers

Old182 said:
Great discussion! If I may be so bold to add my $0.02....All automotive gasolines in this country are manufactured under ASTM D 4814 specifications (www.astm.org) and, although each refinery is different, their product meets the same spec and is fungible (compatible with all the others). Vapor pressure, distillation and vapor lock protection are closely monitored by season and region and are regulated by U.S. EPA - not by oil companies and not by octane grade. Although many of us believe vapor pressure is the culprit in vapor lock problems, it is another value used in the industry called T20 V/L: The temperature at which the vapor to liquid ratio is 20:1 in the distillation curve. ... (Sorry for being so nerdy).
Click to expand...

Old182,

Thanks for the clarifications and putting us on to the industry standards business. Surely no need to apologize to me for "being so nerdy"; I think of it as providing facts--which is good!

In case anyone is interested, there is a bible of-sorts regarding this stuff that you can see through Google Books. Here's the link:

http://books.google.com/books?id=J_...onepage&q=vapor lock standard T20 V/L&f=false

The vapor lock discussion is around page 78. Also, contains a lot more details about the butane and ethanol issues discussed earlier.

The standard involving the temperature at which the vapor/liquid ratio is 20 was apparently developed based on conditions under which diaphragm type fuel pumps for carbureted engines start having issues causing stalling or running rough. I was interested to see that they seem to define "vapor lock" as including running rough. I had assumed it meant engine "locked" or completely shut down. So, I guess I've had more true vapor lock issues than I realized after all.

Steve
 
Thanks, Steve. Another tidbit that might shed more light on these problems: In SAE's Automotive Fuels Reference Book, 2nd Edition, page 180, it explains the phenomenon of Carburetor Foaming: "...caused by the rapid boiling of fuel as it enters a hot carburetor, thereby generating a foam which causes the float to sink. This allows more and more fuel to enter the bowl so that it fills with foam, thereby blocking the air vent and causing an increase in pressure inside the bowl. This pressure increase, in turn, forces excess fuel through the metering jet and vent so that the vehicle suffers similar malfunctions to those caused by vapor lock, even though they are caused by excessive enrichment of the mixture rather than the overleaning that occurs with vapor lock. In cases where the vent goes directly to atmosphere, fuel can be forced out into the engine compartment and cause a fire hazard." Sound familiar? I do remember vapor lock (or was it carb foaming?) problems with my diaphragm fuel pump small block Chevy with lopey cam, headers, etc. until I installed an electric fuel pump in the trunk to feed it. Problem solved. I spoke with several Model A folks from our club today at a car show and they have seen bubbles in clear filters and one had fuel bubble from the carburetor vent on their engines, but neither experienced vapor lock. Hmmm.
 
Old182 said:
Thanks, Steve. Another tidbit that might shed more light on these problems: In SAE's Automotive Fuels Reference Book, 2nd Edition, page 180, it explains the phenomenon of Carburetor Foaming: "...caused by the rapid boiling of fuel as it enters a hot carburetor, thereby generating a foam which causes the float to sink. This allows more and more fuel to enter the bowl so that it fills with foam, thereby blocking the air vent and causing an increase in pressure inside the bowl. This pressure increase, in turn, forces excess fuel through the metering jet and vent so that the vehicle suffers similar malfunctions to those caused by vapor lock, even though they are caused by excessive enrichment of the mixture rather than the overleaning that occurs with vapor lock. In cases where the vent goes directly to atmosphere, fuel can be forced out into the engine compartment and cause a fire hazard." Sound familiar? I do remember vapor lock (or was it carb foaming?) problems with my diaphragm fuel pump small block Chevy with lopey cam, headers, etc. until I installed an electric fuel pump in the trunk to feed it. Problem solved. I spoke with several Model A folks from our club today at a car show and they have seen bubbles in clear filters and one had fuel bubble from the carburetor vent on their engines, but neither experienced vapor lock. Hmmm.
Click to expand...

Old182,

The phenomenom you describe above is commonly referred to in the MoToR's and Chilton's manuals of the '40s & '50s, as "percolation", and was a fairly common problem with down-draft carbs.

This is the first time I've heard it described as "foaming", but the symptoms jive with percolation.

The only vehicles I had a consistent percolation problem with were 216 & 235 Chevy sixes running the Rochester B carburetor. When it occurred, it was always as a "hot start" problem: come back to the vehicle after a five or ten minute stop in hot weather, and the engine doesn't want to start.

The "smoking gun" is when the vehicle finally starts, it usually belches a cloud of black smoke until the excess fuel is cleared.
 
Old182 said:
Thanks, Steve. Another tidbit that might shed more light on these problems: In SAE's Automotive Fuels Reference Book, 2nd Edition, page 180, it explains the phenomenon of Carburetor Foaming: "...caused by the rapid boiling of fuel as it enters a hot carburetor, thereby generating a foam which causes the float to sink. This allows more and more fuel to enter the bowl so that it fills with foam, thereby blocking the air vent and causing an increase in pressure inside the bowl. This pressure increase, in turn, forces excess fuel through the metering jet and vent so that the vehicle suffers similar malfunctions to those caused by vapor lock, even though they are caused by excessive enrichment of the mixture rather than the overleaning that occurs with vapor lock. In cases where the vent goes directly to atmosphere, fuel can be forced out into the engine compartment and cause a fire hazard." Sound familiar? I do remember vapor lock (or was it carb foaming?) problems with my diaphragm fuel pump small block Chevy with lopey cam, headers, etc. until I installed an electric fuel pump in the trunk to feed it. Problem solved. I spoke with several Model A folks from our club today at a car show and they have seen bubbles in clear filters and one had fuel bubble from the carburetor vent on their engines, but neither experienced vapor lock. Hmmm.
Click to expand...

You solved your problem because you shortened the suction line of your fuel pump and most likely took it away from running near any heat source under the car. Also you used an electric fuel pump that had more pressure to over come any blockage in the discharge line. You solved your problem! A real source of repair. Not the mickey mouse / band aid fix that I'm hearing on this thread.
Please give me and the "non believers" the reason the guys you spoke to in your club That didn't experience vapor lock.
On another note I was out driving today in 90 degree weather with the same crap fuel everybody else uses in stop and go traffic and my car ran fine. I did notice that temperature of the coolant went as high as 185 degrees.
I'm going to wait until we get a really hot day and I'm going to clamp the wife's oven thermometer to the fuel line and see what the fuel line/engine compartment is running at. I'm just curious. I will post the results when that happens.
 
Good idea. I bought a Sears IR thermometer to solve another problem and will take it with me today to be in parade in Florida, NY. It's hot and humid (bet we get wet) and will check the temp of fuel at the filter, line, and carburetor right after. I'll be with the club member who experienced the boiling through the vent during a parade. That turned ugly when he took off from a stop with spark retarded, heard a backfire, and found his carburetor was on fire! With a carburetor attached to a cast iron intake manifold attached to a cast iron exhaust manifold and no cooling air flow, things can get nasty in a hurry. More to come....
 
FWIW: Glass bowl temp after the parade was ~120F, steel fuel line was ~140F, carburetor was ~155F-165F. Radiator surface temp was a little over 200F and ambient temp was 89F with humidity off-scale. The little bugger never missed a beat or hestitated during the ~2 mile drive with both levers all the way up, 1st gear at ~1-2 mph, and 2 blade steel fan. It did way better than I did (but that's why God made cold beer for us). I'm sure there could have been boiling in the carburetor at those temperatures, but we didn't notice it if there was. Rechecked temps after the highway trip home and temps were very close to those at the parade except the radiator was ~170F. The other Model A with an IR thermometer had similar temps at the parade but none of the 4 Model As in the parade had any problems. What great cars!
 
Thanks for the information. Tomorrow I'm supposed to go to a car show/swap meet at Flowrerfield in St. James. Perhaps we'll have the same weather as today on Long Island (Hot & Humid). I'll try to run the same test as you did and post the results.
I'm posting pictures of my arsenal of tools for the test.
 
Last edited:
Special Coupe Frank said:
Old182,

The phenomenom you describe above is commonly referred to in the MoToR's and Chilton's manuals of the '40s & '50s, as "percolation", and was a fairly common problem with down-draft carbs.

This is the first time I've heard it described as "foaming", but the symptoms jive with percolation.

The only vehicles I had a consistent percolation problem with were 216 & 235 Chevy sixes running the Rochester B carburetor. When it occurred, it was always as a "hot start" problem: come back to the vehicle after a five or ten minute stop in hot weather, and the engine doesn't want to start.

The "smoking gun" is when the vehicle finally starts, it usually belches a cloud of black smoke until the excess fuel is cleared.
Click to expand...

From what I just read in my '35-'50 motors manual under "Carter" It seems that this only happened after the car was shut down and the vapor rose into the main nozzle and pushed the fuel into the venturi and in turn emptied the float chamber into the manifold. This flooded condition will cause hard starting. So they put a anti-percolating unit on the carburetor. This was basically a vent system. Your 100% right on the "Smoking gun"
 
check the steel fuel line to see if it is absolutely clear of rust particles sticking to the walls of the tubing , as the gas flows past it will create turbulance and drag on the fuel as it passes over the obstruction.
 
Well I was somewhat disappointed today, No traffic and not so hot for my test. These are my results:
Glass bowl Temp. 108*
Steel fuel line 151*
Carburetor 141*
Upper Radiator surface 179*
Ambient temperature 84* and very humid
Highway temp. running ( fuel line) 116*
Although some temperatures match "Olds182", It just wasn't hot enough.
The wife won't let me use her oven thermometer anymore, she told me she'll take my temperature with it if I tried again!!! I'm posting some actual pictures while I was driving.I took one when I was Idling for twenty minutes with the spark retarded all other times the spark was advanced about 5/8's down. . You can tell by the speedometer and temperature gauges what was going on.
 
Last edited:
This my first post on the new Ford Barn. Finally I was approved today. There have been several very good posts by people who obviously have some Chemical Engineering experience that are leading them in the right direction. I have more than 30 years experience in the refining industry, mostly in gasoline component refining for a company that licenses refining processes.

There are many factors involved in formulating gasoline. Gasoline is formulated for modern cars with fuel injection and pumps in the tank. This increases the fuel pressure. Higher pressure will inhibit vaporization. Modern cars have high underhood temperatures, higher than our Model A's.

The important factor to consider is Reid Vapor Pressure (RVP). Over the last 25-30 years refiners have had to control RVP at the direction of the EPA. RVP is a variable that is somewhat different for every market in the US. The addition of various components will change the vapor pressure. The best components are most expensive. A few tenths of a cent per gallon really makes a difference in the refiners cost and the profitability of the single most important product of any refinery.

You should use an infrared non-contact thermometer to take the temperature at various places in the engine compartment, especially the carburator bowl just after shutting off the engine. I expect that the temperature will show a drop as the gasoline in the carburator bowl is boiled off. This should happen in cars that show problems with "vapor lock".

I have just written an article for the Smoky Mountain Model A Club that will be published in a few weeks. There is enough interest in this subject that I should do some hands on research and review the written materials prior to writing an article for one of our magazines. This might take a few months. I hope that it will be published by the end of the year. Meanwhile, if you are experiencing problems or want to do a little preventative work for vapor lock insurance you should insulate your fuel line with rubber fuel hose and flex electric loom over the rubber line. Carefully split the rubber line and install it on the metal line. I am looking at a light gauge metal shroud for the carburator. All of this should be easily removable for judging.

Any comments are welcome, either directly to me or by posting them.

Thanks.

Vic in E-TN
 
You must log in or register to reply here.
Back
Top