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Serious Vapor Lock

Old 01-06-2019, 03:44 PM
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Serious Vapor Lock

Iíve got an Ď86 LG4 that quits if I drive it on a warm day, shut the engine off for a few minutes and then drive it again. I had it die on me once as I left the gas station. I found that I could start it immediately if I pour cold water on the fuel line leading to the fuel pump. I minimized the problem by insulating the fuel line. The exhaust manifold isnít far away and gets as hot as 500 degrees. How did these cars ever leave the factory like this? It doesnít get that warm where I live. Is there supposed to be some kind of a shield on the exhaust or fuel line side to prevent the heat from warming up the fuel? Is there anyone selling something similar to GMís part # 14085385 low pressure helper pump kit? There doesnít appear to be any restriction from the tank to the pump. Flows plenty of fuel when cold.
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Old 01-06-2019, 03:59 PM
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Re: Serious Vapor Lock

Your problem isn't"vapor lock". It's the EXACT OPPOSITE of vapor lock.

It is the LIQUID fuel getting hot and forcing too much of itself into the carb, at which point it boils into a foam like a shaken-up Diet Coke, and spewing out of every hole in the carb.

Insulate the fuel pump from the block to solve it. 2 gaskets usually does the trick.

It's also not about how the car left the factory. It's about how fuel today is quite a bit different from what our antique cars were born into.
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Old 01-06-2019, 04:13 PM
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Re: Serious Vapor Lock

Originally Posted by sofakingdom View Post
Your problem isn't"vapor lock". It's the EXACT OPPOSITE of vapor lock.

It is the LIQUID fuel getting hot and forcing too much of itself into the carb, at which point it boils into a foam like a shaken-up Diet Coke, and spewing out of every hole in the carb.

Insulate the fuel pump from the block to solve it. 2 gaskets usually does the trick.

It's also not about how the car left the factory. It's about how fuel today is quite a bit different from what our antique cars were born into.
I donít think thatís happening. The carb is completely dry after it runs out of fuel and if I take off the pump inlet fuel line thereís not a drop of fuel in it. Since pouring cold water on the fuel line gets me going Iíd say that fuel line is vapor.
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Old 01-06-2019, 04:36 PM
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Re: Serious Vapor Lock

the fuel lines can be insulated but your problem should not be quite so persistent.

the stock pump should recirculate fuel constantly through the lines and alleviate 'vapor lock' under all but severe conditions. your supply line is clear, but is your return line? have you checked the flow of your pump? I've had them fail before where they would barely move fuel (the fulcrum arm in the pump had started to come out of it's peened housing within the pump body-hard to put into words but it was evident upon inspection).
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Old 01-06-2019, 06:35 PM
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Re: Serious Vapor Lock

Originally Posted by naf View Post
the fuel lines can be insulated but your problem should not be quite so persistent.

the stock pump should recirculate fuel constantly through the lines and alleviate 'vapor lock' under all but severe conditions. your supply line is clear, but is your return line? have you checked the flow of your pump? I've had them fail before where they would barely move fuel (the fulcrum arm in the pump had started to come out of it's peened housing within the pump body-hard to put into words but it was evident upon inspection).
The return line is also clear. When I ran into this problem I replaced the pump with a new Spectra Premium with no change in symptoms. Insulating fuel line helped quite a bit but it still hesitates badly after a hot start until fuel has started moving through the lines. This is why I suspected that a heat shield is missing somewhere. I plan to add ceramic coated headers. That ceramic coating makes a noticeable difference. After a hard run with the Cutlass and the engine still running, my headers are 180 degrees vs 500 degrees for the exhaust manifolds on the Camaro.
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