Vapor Lock

Dave in MN said:
We were on tour late last summer during a hot spell. In general, those that filled up with 10% ethanol gas had problems while those that filled with premium non-ethanol kept on cruising. The problem cars were balking, backfiring, hard starting and losing power. There was one gent that used 10% ethanol gas but added a few ounces of two cycle oil to his gas. He had no problem...we added some Marvel Mystery oil to a couple cars that were having problems and the issues went away. A question for those that understand the chemical result of adding this product to the ethanol gas: Did the addition of the oil to the gas solve the problem or was it just chance that they improved?
Thanks for any comments!
Good Day!
Dave in MN
Click to expand...

I'm as skeptical about these additives as others are about the whole vapor lock business; I would have to see it with my own eyes, and have to be convinced that the additive was the ONLY thing that changed. All I know for sure is that Marvel Mystery Oil didn't help me. Neither did adding some diesel fuel, which was a fashionable remedy several threads ago, sworn to by several folks. It remains a total mystery why some Model A's have the problem while others never do. For various reasons, I have tested numerous distributor/ignition systems, fuel filters, and carburetors, two radiators, three fans, two motor rebuilds, and a centrifugal advance system. Insulating the fuel line helped, but only the "new" Zenith carb really made a big difference--also doesn't die on hard stops, BUT, it's not without disadvantage--noisy.

The increased vapor pressure upon addition of ethanol was a major challenge to the oil industry when the mandate to "oxygenate" fuels for pollution control went out. Eventually, with the strong encouragement of the corn lobby, the composition of other ingredients was adjusted sufficiently so that increased hydrocarbon/photochemical smog cost due to increased volatility did not wipe out the cleaner-burning oxygenation benefit. In my cynical opinion, it is the corn lobby that is the tail wagging the dog in this matter, and nothing will change as long as Iowa has the first presidential primary election.

Steve
 
Last edited:
sphanna said:
I have heard guys complain about "vapor Lock" and others say that a gravity feed system cannot vapor lock. In any case here is what does happen in my car. In hot wx and after a full temperature warm up drive and then I stop for a time for a snack or such, I can restart the car and get about a block down the road and it will quit. I have discovered that I can loosen the 5/8 head plug on the front of the top casting of the carb and I get a hissing of escaping vapor. Let it escape and retighten and I am off again. What happens is the fuel in the float chamber or above it boils when sitting with no fuel flow while stopped. This boiling fuel forces fuel an "air" or vapor gap in the fuel supply. It releases when the plug is loosened and then when restarted ,which it will immediately, the fresh cool fuel prevents the carb fuel to overheat. This used to haunt me on tours in hot weather. I used to have to wait maybe 20 min. to get it to start again. Now It is so easy to fix that it is no problem to me.
Click to expand...


Look at 12min in to this video, 160F the gasoline boiled https://www.youtube.com/watch?v=d7AkcjnCTVU
 
ford1 said:
you dont get vapor lock on gravity feed carbs, the fuel runs down hill no matter what, if it hard to start after a long run the fuel is probably being evaporated or boiled in the carb causing a rich starting problem, they make a heat shield that goes between the carb and manifold mount, it deflects heat away from the carb, check all the fuel delivery system, make sure none are restricted, might even be an electrical problem
Click to expand...

Wrong....

I have had good luck with using Marvel Mystery Oil as an additive to my gas. I use the amount in the directions and it really helps with Vapor Lock.

Marc
 
How about running a cool can or homemade equivalent ???? Hot rodders use them to improve performance. Basically coiled tubing in a can with a top - place it between the sediment bowl and the carb - fuel will be 32 degrees going into the carb keeping things nice and cool. Carry xtra ice in a cooler.....
 
im still wondering how do you vapor lock a gravity fed sysyem, I system with a fuel pump will vapor lock when the fuel pump looses suction and stops pumping fuel because of fuel boiling in the pump, I just don't see a gravity feed system suffering that problem, I can see if the carb gets so hot it boils the fuel out of it, but that's not vapor lock
 
My story....

Car : Original Model A Fuel Setup
Temp: 100 F (In the Shade)
Driving Condition : 20 minutes at 50 MPH, then stop for a traffic light
Engine Problem : As the car rpm dropped to idle the car started to run rough. I had no power. I opened up the GAV 1 to 2 turns and the engine power returned some. As I got back up to speed, the engine power returned and I returned the GAV to the normal position.


I had a similar problem after pulling into a Gas station. When I tried to start and pull away, no power until I opened up the GAV again. After moving some, power returned.

After using MMO (Marvel Mystery Oil) in the gas, this hasn't happened again.

I call it Vapor Lock. Maybe the gas was boiling in the carb....

MMO helps.

Marc
 
I am certainly no fan of ethanol, but in California that is all we have.....period. I have had my Model A for about 8 years now, stock with 5.5 HC head. To date, I have had zero problems with my car ever, that I could attribute to the fuel. I also use MMO as recommended, but do not know if it helps with that. I get a chance to drive on many hot days, and have even driven over the 5,000' Grapevine (Cajon Pass) on a 90+ day, and no running problems at all. The only thing I can really complain about with the ethanol is that mileage is not quite as good.
Terry
 
I have the same problem and always with 1 1/2 " fuel left and after quite a hard run and am back to travelling light. Immediately put some more gas in it and she'll start. I don't think the weight of fuel is adequate to push the fuel through when its hot. I'm thinking of attaching a way to pressure the tank momentarily to see if Im right.
 
After read this thread and these from a while back:

http://www.fordbarn.com/forum/showthread.php?t=37710&showall=1

http://www.fordbarn.com/forum/showthread.php?t=37710&showall=1

This totally reminds me of what I observed as a kid with my Dad' 8N Tractor which is much like my model A (carb wise)

http://cloudlakes.com/data_images/models/ford-8n/ford-8n-04.jpg

I took my car for 2, 12 miles drives in city traffic yesterday and took the temperature of the carburetor and the fuel lines after I turned off the engine:

Zenith 1 : 112F
Fuel lines: 90F near the Zenith 1.

So if fuel will boil in to vapor, at those temps. I can see an issue... So one could either open the fuel line to the Zenith 1 as Tom posted, or let the vapor by cracking open the 5/8 Zenith 1 filter plug or let it cool, or slowing put a little water on the Zenith 1.
 
As much as I hate ethanol, I don't think it is the main modern problem. Today's fuel, blended for high pressure injector pumps and vapor containment systems, vaporizes at a much lower temperature than the 'old' pre-cat crack fuels. The problem is the light fractions in the blend. The main culprit: butane, a four carbon product that is produced during cracking in significant quantities and hard to sell off by itself. They stuff as much butane into the 'gasoline' as a seasonal area blend will allow. In Chicago the winter blend fuel can be 25% or more butane. That gas will practically boil in your hot hand! Sure, cars start at -20F with a tank full, but if you put your A away in December with a tank of the stuff and then take it out in May on a warm day you will have problems.

A modern car with a closed vapor system, submerged tank pump, and fuel line pressurized to 50 psi doesn't care. They just don't make gravity/ carburetor friendly automotive fuel anymore. Lawnmowers and other carbureted small engine devices can get away with the modern gas because their open design does not have the underhood heat concentration problem.
 
It does make a person wonder what they did back in the 30's when the "Corn Alcohol Gas" brand (at 10 percent blend) was sold in the Midwest. And the alcohol injection jars sold by the various speed shops and JC Whitney back in the 60's.
If indeed these blends are creating problems for people there must be something else going on. I leave gas in everything over the long winter months here in the Northeast (and in the snowblower all summer - March to December). I left a half tank of gas in a '62 BelAir 283V8 for over a year without starting it up. Turn the key, pump the gas and go.
I wonder if the blends differ in different parts of the country (I'm in upstate NY).
 
You must log in or register to reply here.
Back
Top