Vapor Lock?
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5th Wheeling
Joined: May 2013
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Vapor Lock?
The last couple times I took my '51 F1 with 226 fh6 out mid day, after I warmed up the engine it drove okay for a few minutes, then lost all power, idled rough, on 3 or 4 cyls. Shut it down and waited 5 to 10 minutes, it started and ran fine again. Both times were hot days (high 90s). First time, I limped it back home. The second time I went 3 miles (shutting it down 3 or 4 times) and left it at a safe location overnight. Next morning, much cooler, started it up and drove it home, no issues. I described the problem to a local guy who has a carb rebuild business and he said it could be vapor lock. Is this vapor lock? I've read up on it some and it seems possible. The two suggestions I've read for dealing with it are insulating the fuel lines and installing an electric fuel pump. Anyone done either or both of these to cure vapor lock? Would rather not drill holes in the truck, but is insulating alone a waste of time?
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5th Wheeling
Joined: May 2013
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Thanks! I just bought the truck about a month ago. I drove it from the place of purchase around 75 miles to my place and since then have driven it on weekends on trips of between 5 and 20 miles. It's only been a problem on these last couple of hot day outings. The previous owner replaced the fuel pump not too long ago.
Cargo Master
Joined: Apr 2005
Posts: 3,337
Likes: 165
From: Harpswell Maine
An old trick that I used in the past was to put a number of clothes pins (wooden) on the steel fuel line. Just clip them on maybe about 10 of them. I did it on my 49 years ago on a cross country trip, it worked.
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5th Wheeling
Joined: May 2013
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Interesting. In my case it seems like where the line is most likely to get too hot it is rubber or something like it. But yes, I can see how that would work to conduct heat away from the steel.
Posting Guru
Joined: Sep 2012
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On the contrary! The steel conducts heat well compared to the rubber. Lick the two on an ice-cold Montana morning and tell me otherwise. 
Anyway, wooden clothes pins do not serve as a heat sink. Rather, they serve to insulate the steel line from the high temperature ambient air in the engine compartment. I have my fuel line covered with pipe insulation (AKA: "donkey Донг"). No worries regarding vapor lock ever again.
Also, make sure that the fuel flow isn't restricted by a clogged filter or rust/crud in tank. The lowered pressure that a restriction causes on the inlet side of a fuel pump will greatly aggravate vapor lock tendencies.
Anyway, wooden clothes pins do not serve as a heat sink. Rather, they serve to insulate the steel line from the high temperature ambient air in the engine compartment. I have my fuel line covered with pipe insulation (AKA: "donkey Донг"). No worries regarding vapor lock ever again.
Also, make sure that the fuel flow isn't restricted by a clogged filter or rust/crud in tank. The lowered pressure that a restriction causes on the inlet side of a fuel pump will greatly aggravate vapor lock tendencies.
Elder User
Joined: Feb 2013
Posts: 518
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From: Crystal Lake
If its vapor lock, it should be rather easy to resolve. Make sure your gas line is not too close to the engine, and make a base for your carb with either multiple gaskets, or a metal spacer, about 1/4" thick. You probably have a boarder line heat issue with your carb or lines that only creates vapor lock when the heat is excessive. That's why the cloths pins worked. They created insulation.
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5th Wheeling
Joined: May 2013
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On the contrary! The steel conducts heat well compared to the rubber. Lick the two on an ice-cold Montana morning and tell me otherwise.
Anyway, wooden clothes pins do not serve as a heat sink. Rather, they serve to insulate the steel line from the high temperature ambient air in the engine compartment. I have my fuel line covered with pipe insulation (AKA: "donkey Донг"). No worries regarding vapor lock ever again.
Also, make sure that the fuel flow isn't restricted by a clogged filter or rust/crud in tank. The lowered pressure that a restriction causes on the inlet side of a fuel pump will greatly aggravate vapor lock tendencies.
Anyway, wooden clothes pins do not serve as a heat sink. Rather, they serve to insulate the steel line from the high temperature ambient air in the engine compartment. I have my fuel line covered with pipe insulation (AKA: "donkey Донг"). No worries regarding vapor lock ever again.
Also, make sure that the fuel flow isn't restricted by a clogged filter or rust/crud in tank. The lowered pressure that a restriction causes on the inlet side of a fuel pump will greatly aggravate vapor lock tendencies.
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5th Wheeling
Joined: May 2013
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If its vapor lock, it should be rather easy to resolve. Make sure your gas line is not too close to the engine, and make a base for your carb with either multiple gaskets, or a metal spacer, about 1/4" thick. You probably have a boarder line heat issue with your carb or lines that only creates vapor lock when the heat is excessive.
Fleet Mechanic
Joined: Aug 2010
Posts: 1,994
Likes: 3
From: Morgan Hill, CA
If you're getting vapor lock now and it didn't happen in the past, consider what might have changed.
If the gas in the tank is "winter" gas, that would mean that the vapor pressure of the fuel could be higher....that makes the gas more volatile, and more prone to vapor lock. If the gas is old, the chemicals added to reduce vapor pressure can dissipate...making the fuel more prone to vapor lock.
All of that said, vapor lock usually happens in the suction side of the fuel system. At reduced pressure, the fuel can effectively boil at a lower temperature. An electric fuel pump close to the gas tank will make it so that most of the system is under pressure rather than under a vacuum.
If it were me, before I took drastic action, I would drain the tank and put in fresh gas & give it a try.
Dan
If the gas in the tank is "winter" gas, that would mean that the vapor pressure of the fuel could be higher....that makes the gas more volatile, and more prone to vapor lock. If the gas is old, the chemicals added to reduce vapor pressure can dissipate...making the fuel more prone to vapor lock.
All of that said, vapor lock usually happens in the suction side of the fuel system. At reduced pressure, the fuel can effectively boil at a lower temperature. An electric fuel pump close to the gas tank will make it so that most of the system is under pressure rather than under a vacuum.
If it were me, before I took drastic action, I would drain the tank and put in fresh gas & give it a try.
Dan
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5th Wheeling
Joined: May 2013
Posts: 42
Likes: 0
If you're getting vapor lock now and it didn't happen in the past, consider what might have changed.
If the gas in the tank is "winter" gas, that would mean that the vapor pressure of the fuel could be higher....that makes the gas more volatile, and more prone to vapor lock. If the gas is old, the chemicals added to reduce vapor pressure can dissipate...making the fuel more prone to vapor lock.
All of that said, vapor lock usually happens in the suction side of the fuel system. At reduced pressure, the fuel can effectively boil at a lower temperature. An electric fuel pump close to the gas tank will make it so that most of the system is under pressure rather than under a vacuum.
If it were me, before I took drastic action, I would drain the tank and put in fresh gas & give it a try.
Dan
If the gas in the tank is "winter" gas, that would mean that the vapor pressure of the fuel could be higher....that makes the gas more volatile, and more prone to vapor lock. If the gas is old, the chemicals added to reduce vapor pressure can dissipate...making the fuel more prone to vapor lock.
All of that said, vapor lock usually happens in the suction side of the fuel system. At reduced pressure, the fuel can effectively boil at a lower temperature. An electric fuel pump close to the gas tank will make it so that most of the system is under pressure rather than under a vacuum.
If it were me, before I took drastic action, I would drain the tank and put in fresh gas & give it a try.
Dan
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5th Wheeling
Joined: May 2013
Posts: 42
Likes: 0
Thanks for your response. Filter is between the tank and the pump. Previous owner had recently put in a new coil. I know that what seem like fuel problems can turn out to be ignition system, but it fires up after 5 minutes and idles smooth, so I'm leaning towards a fuel issue.
