Gas Boiling

leadpot

leadpot

Senior Member
When the car is shut off the carb leaks gas. I can usually hear the gas boiling in the carb and then starts leaking. Does this do any damage to the carb by the gas becoming pressurized & being forced out.
Is there a fix for this besides letting the car idle until it dies, besides I still get a little fuel leak and smell sometimes when doing this.

Stock 29 tudor - nothing but ethanol gas in my area, makes no difference what grade is used and always add MMO
It is not the float in the carb, have tried 4 different carbs including 2 new ones, all do it.
Timing is good, water temp runs 190 - 200 on hot days. Splash pans are in place.
If this was this an issue when the cars were new think ford would have had a fix, or is it just the crap gas & something we have to live with?
 
How did you determine the 190-200f temperatures? Where do you put your timing advance lever when at 35-40 MPH? Do you have access to an infrared gun to check the efficiency of the radiator. Sounds like you are on the ragged edge of producing too much heat and not able to get rid of nearly enough. Many many threads on overheat, use the advance search above for some ideas.
 
Most feel this is due to the ethanol in the gas. I'm not sure if this has been proven by those that have access to non-ethanol gas, good question perhaps.

I'm also not sure the verdict is in yet. No one is really sure why this happens.

Some have even blamed the glass sediment bowl as a suspect problem. I don't know, does that mean the later cast iron is better?

There have been several recommended fixes for this, not sure if they have been successful:

Phenolic Carburetor insulator to insulate the carburetor from the manifold
(can be found on ebay)
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Heat shield to shield carburetor from exhaust manifold heat (there are posting on Ford Barn with photos)
Model A Heat Shield 2.jpg

Some have changed the two blade fan to a four blade or six blade plastic. I don't think that has helped. From what I understand the two blade works better than the four blade, and the six is only slightly better than the two.

Some have insulated the fuel lines using aluminum foil. There are after market products that are designed to wrap around the fuel lines and insulate them as well. Not sure if that helps.

I experimented myself and installed a heat shield along with a small low voltage fan and a heat sink attached to my Tilly carburetor. The fan comes in handy when you stop the car. The fan is left on, controlled by a small switch under the dash, it uses very little battery power, and it quickly cools down the carburetor. Great for short stops. When you get back in the car, the carburetor is cool and the engine starts up right away. You may not like the look of this. I don't, but it works.
IMG_2864.jpg
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A couple of days ago after I turned off the car and maybe 10 minutes later I could actually hear what sounded like the fuel boiling.

I always thought that only happened with high performance cars where the carb is sitting on top of the intake on top of the engine. My other cars will gain about 20 degrees in temp after 10-15 minutes.
 
A lot has to do with how much pentane and butane is in the fuel, not the ethanol. Pentanes and butanes vaporize at a much lower temperature than gasoline (iso-octane) and ethanol.

I ran into this problem a few years ago and I found if I left my gas 'on' while stopped for a short while it didn't boil. For longer periods I would shut of the gas and run the carb dry.
 
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Wow Zener, you really put some thinking into your setup. Like the heat shield idea, may try that along with the spacer
 
I have the carb shield on my Zenith, but it will still boil fuel if the timing is off. Timing is good, no boil.
 
I would think that if it was the ethanol in the fuel that all of us that use E10 would experience the same thing. I for one use E10 and have no such problem. When we hang all our issues on ethanol, we never find the REAL problem.
 
"Timing is good"

how do you know that?
I am betting it is late

many many threads on this a search will be revealing
we have the same questions and the same typing repeatedly
 
Well, here in California we have no option to not use ethanol......period. I also have a glass sediment bowl, and no heat shielding added, and drive my Town Sedan in 100 degree weather with no sign of vapor lock or fuel boiling. None of us likes "crap" gas, and would prefer not to use it, but I do not know of a single Model A owner in our club that has any issues that have been blamed on it. Like we have mentioned before, if ethanol caused all these problems, Model A's in states that have mandates to use it would be either parked or just running poorly. It is an easy target instead of finding out the real cause.
 
TerryH said:
Well, here in California we have no option to not use ethanol......period. I also have a glass sediment bowl, and no heat shielding added, and drive my Town Sedan in 100 degree weather with no sign of vapor lock or fuel boiling. None of us likes "crap" gas, and would prefer not to use it, but I do not know of a single Model A owner in our club that has any issues that have been blamed on it. Like we have mentioned before, if ethanol caused all these problems, Model A's in states that have mandates to use it would be either parked or just running poorly. It is an easy target instead of finding out the real cause.
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ya pretty much all we can get around here is e10 and that's the way its been for years. Cant say we have had any problems with fuel delivery in engines that couldn't be just old age, loose bolts, or dirt in it.
 
TerryH said:
Well, here in California we have no option to not use ethanol...... I do not know of a single Model A owner in our club that has any issues that have been blamed on it.
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The decrease in mileage is the biggest problem I have with ethanol. Ethanol has less BTUs per gallon and simply does not make a much power as gasoline. Therefore you have to use more ethanol to get the same result.

You would think the government would be looking for a more efficient fuel, not mandating a less efficient fuel.:p:p

http://zfacts.com/p/436.html
 
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Y-Blockhead said:
The decrease in mileage is the biggest problem I have with ethanol. Ethanol has less BTUs per gallon and simply does not make a much power as gasoline. Therefore you have to use more ethanol to get the same result.

You would think the government would be looking for a more efficient fuel, not mandating a less efficient fuel.:p:p

http://zfacts.com/p/436.html
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True, but with E10 (10% ethanol) which is what most of us use, the drop is not significant...E85 or 100% ethanol, yes, but not E10...

"In general, vehicle fuel economy may decrease by about 3% when using E10 relative to gasoline that does not contain fuel ethanol."

http://www.eia.gov/tools/faqs/faq.cfm?id=27&t=4

...if you get 21 MPG with pure gasoline, you would get 20.4 MPG with E10. I doubt if that difference could be actually measured. I know, I know, there will be some that claim a huge drop in MPG, but the science just isn't there to support that.



Although there are all kinds of reasons that we have to live with E10 (political and otherwise), one major one is that ethanol is a low cost oxygenator that replaced MTBE when MTBE was found to be rather harmful to us humans (and other living things).

"Advocates of both sides of the debate in the US sometimes claim that gasoline manufacturers have been forced to add ethanol to gasoline by law. It might be more correct to say they have been induced to do so, although any oxygenate would fulfill the law."

https://en.wikipedia.org/wiki/Methyl_tert-butyl_ether

One reason non ethanol gas is expensive is that using an approved oxygenator other than ethanol is expensive. If someone could come up with an oxygenator less expensive than ethanol that doesn't grossly pollute, I think you'd see lots of non-ethanol laced fuel. Of course then we'd be complaining about the NEW oxygenator and blaming all our driveabilty issues on it. ;)
 
I like both the heat shield and carb spacer. Another thing I think helps is to make sure the fuel line always runs downhill and some judicial bending may be necessary to make that happen.

I run non-ethanol in all the small engines, but, the Model A gets anything. It almost always gets non-ethanol [10%] and all the old stale fuel. It really doesn't care what I feed it.
 
leadpot said:
When the car is shut off the carb leaks gas. I can usually hear the gas boiling in the carb and then starts leaking. Does this do any damage to the carb by the gas becoming pressurized & being forced out.
Click to expand...

Boiling fuel does no harm to the carb. It is not significantly pressurized.

Based on your numbers, it sounds to me like your engine is running hot. It could be the radiator, it could be ignition timing, it could be something else.

YMMV.

.
 
Gas without the corn crap is better, but all of today's gas boils at a lower temperature than it did in the 70's and earlier. A heat shield between the carb and exhaust manifold is a big help.
 
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