The Ford Barn

Bob Johnson · 01-03-2016, 01:56 AM

I have had a problem several time with my Model A. I would not call it vapor lock. It happens when I slow down or more often when I stop right after a long run at speeds over 50 mph on a hot day. Here in California we have winter and summer gas. It happened once in December when we had a very hot week, over 80 degrees. I think it was because the winter gas boils out of the carburetor easier than the summer gas. When it happens all I have to do is open up the GAV and everything is fine. Depending on how bad it is I have to open the GAV 1 to 3 turns. After a couple of minutes I can turn down the GAV. One time I was going up a long steep grade. I have to open up the GAV 1 to 1.5 turns to keep the engine running right. Once I got over the hill I stopped for gas and the carburetor was so hot a drop of water would instantly sizzle and boil off of it. I used a gallon of water to cool down the carburetor. My analysis is that the carburetor gets hot enough to boil the gas. This is most likely to happen when you pull off of the highway and come to a stop. The residual heat in the engine super heats the carburetor. Since the gas has vaporized in the carburetor not enough can get through the main jet and the mixture is too lean. By opening up the GAV there is a second jet supplying gas and the mixture is corrected. Once the carburetor has cooled the gas is no longer boiling and the GAV can be turn down.

I do not have engine splash pans. Perhaps they might help the air flow to the carburetor and prevent the boiling gas.

Bob

01-03-2016, 01:56 AM	#22
Bob Johnson Senior Member Join Date: May 2010 Location: California Posts: 1,021	Re: Vapor lock I have had a problem several time with my Model A. I would not call it vapor lock. It happens when I slow down or more often when I stop right after a long run at speeds over 50 mph on a hot day. Here in California we have winter and summer gas. It happened once in December when we had a very hot week, over 80 degrees. I think it was because the winter gas boils out of the carburetor easier than the summer gas. When it happens all I have to do is open up the GAV and everything is fine. Depending on how bad it is I have to open the GAV 1 to 3 turns. After a couple of minutes I can turn down the GAV. One time I was going up a long steep grade. I have to open up the GAV 1 to 1.5 turns to keep the engine running right. Once I got over the hill I stopped for gas and the carburetor was so hot a drop of water would instantly sizzle and boil off of it. I used a gallon of water to cool down the carburetor. My analysis is that the carburetor gets hot enough to boil the gas. This is most likely to happen when you pull off of the highway and come to a stop. The residual heat in the engine super heats the carburetor. Since the gas has vaporized in the carburetor not enough can get through the main jet and the mixture is too lean. By opening up the GAV there is a second jet supplying gas and the mixture is corrected. Once the carburetor has cooled the gas is no longer boiling and the GAV can be turn down. I do not have engine splash pans. Perhaps they might help the air flow to the carburetor and prevent the boiling gas. Bob