Air in fuel lines or vapor lock?

989153 · Nov 15, 2019

Hey guys. I have a 65 mustang with an Edelbrock carb. And electric fuel pump and I’m assuming the stock gas tank and metal fuel line

this past week I’ve noticed that when the car heats up it starves itself for fuel and when I look at the clear in line filter there’s tons of bubbles moving through it. Eventually it gets to the point where the engine starves for gas and dies.

ivereplaced all the rubber hoses from the gas tank to the carb, tried a different electric fuel pump and nothing. Does this sound like vapor lock or air being introduced to the line somewhere?

LILCBRA · Nov 15, 2019

It sounds exactly like vapor lock. Usually an electric pump solves the problem, but from what I understand it's used in conjunction with a mechanical pump. The electric is in or near the tank to push fuel to the mechanical pump, then the mechanical pumps it to the carburetor. What pressure is your electric putting out? Carburetors generally like around 6-8 psi. If all else fails, you could install a regulator near the carburetor and increase the pressure from the pump. That would keep the fuel from vaporizing and give you a steady supply of fuel.

stormsedge · Nov 15, 2019

Also, double check your fuel line to ensure it is not too near or on a heat source somewhere.

989153 · Nov 15, 2019

On the package it says 7 but I haven’t gotten around to testing it. I’ve got it mounted in the engine bay as well so I might try putting my spare one near the tank and see if that helps. If not I’ll try insulating the fuel line where they ran it somewhat close to the exhaust

989153 · Nov 15, 2019

stormsedge said:
Also, double check your fuel line to ensure it is not too near or on a heat source somewhere.

That’s my first guess. I’m gonna get some insulating material tomorrow and if all else fails I’ll go through the whole system and make sure everything looks like it should

LILCBRA · Nov 15, 2019

989153 said:
On the package it says 7 but I haven’t gotten around to testing it. I’ve got it mounted in the engine bay as well so I might try putting my spare one near the tank and see if that helps. If not I’ll try insulating the fuel line where they ran it somewhat close to the exhaust

If at all possible I'd try to relocate the fuel lines that run near the exhaust to eliminate that possibility. Insulation works both ways, so if it were to heat your insulating material that material will retain the heat and keep the fuel vaporized longer. And I think if you relocate the pump and mount it near the tank you'll not have any more problems. Pressure helps keep it in liquid form which is why later model fuel injected cars don't have that problem. So moving the pump closer to the tank AND moving fuel lines away from heat sources is the way to go.

rise66 · Apr 29, 2020

Vapor lock and or fuel boiling due to the fuel in todays market boils at a much lower point. My fuel line was so hot your could not even touch it for more than a second. Here's what I have found at this point and the thing I have done.
1. Rebuild the carburetor (helped lower the temp of the fuel line but did not totally fix the problem), Purchased the carb kit from Mikes carburetor. Watch his video's on line.
2. Check the radiator for proper operation. I found mine was circulating but had a lot of blocked tubes due to age. replace the radiator more consistent operating temperature.
3. I installed a phenolic riser insulator raising the carburetor 3/8 of an inch. They also come in 1/2 depending on your clearance. (purchased on Ebay)

All three of these really helped but still not a 100 % fix. So after searching all over the internet and speaking with life long Ford mechanics I ran across you tube videos on vapor lock. I found that in the 60's and the 70's that Ford, Dodge, Plymouth and other used a vapor separator in the fuel line just after the mechanical fuel pump. This returns the access fuel and vapor to the fuel tank allowing a Constance flow of fuel preventing over heating of the fuel. These cars came with a return line to the fuel tank from the factory. This is the same as today with fuel injection has return lines to the fuel tank. This all made since to me so I saw a video of a guy drilling a hole in the sending unit and JB welding it in (not sure I wanted to do that) fixed his problem 100%. So I went on the hunt and found the WIX 33041 vapor separator. I also found out the Ford used three different ones. They had .04, .06, and .08 orifices. The Wix 33041 has a .06 orifice in it and was used on 70 chevys. I also read about electric fuel pumps electric fans but this made the more since to me. I found on EBAY a fuel sending unit for 64 - 68 Mustangs with a 1/4 inch return line built in with a check ball only allowing fuel and vapor to return to the tank sold by MCM products. They also sell them on Summit racing but are twice the price. I also ordered 1/4 aluminum fuel line from Speedway racing parts and the filter from O'reilly auto parts.

Fuel sending unit 39.50
Vapor Separator 8.00
Fuel line 15.00
I will be installing this this coming Tuesday when my buddy's lift is free. I have 100% confidence this will be the cure!!

rise66 · Apr 29, 2020

I installed the Vapor Separator yesterday everything went well, really easy with the aluminum line bending it to match the fuel line. I drove the car reaching operating temperature and continued driving for another 30 minutes with no stalling at stops or sputtering. Turned car off and waited 20 minutes checking for restart problems and listening to the carburetor for fuel boiling. I did not hear any indication that it was, so let's try starting it, fired right up no problem. Next I drove about 30 minutes and stopped to refuel (no ethanol) loosened the gas cap and I could hear the release of pressure so that told me the Vapor separator was operating correctly. Filled the tank went inside to pay and returned. Turned the key and fired right up! So now I will continue driving and look forward to see what happens in 90 degree weather. I due believe I have found the cure!

Adieu · Apr 29, 2020

rise66 said:
Vapor lock and or fuel boiling due to the fuel in todays market boils at a much lower point. My fuel line was so hot your could not even touch it for more than a second. Here's what I have found at this point and the thing I have done.
1. Rebuild the carburetor (helped lower the temp of the fuel line but did not totally fix the problem), Purchased the carb kit from Mikes carburetor. Watch his video's on line.
2. Check the radiator for proper operation. I found mine was circulating but had a lot of blocked tubes due to age. replace the radiator more consistent operating temperature.
3. I installed a phenolic riser insulator raising the carburetor 3/8 of an inch. They also come in 1/2 depending on your clearance. (purchased on Ebay)

All three of these really helped but still not a 100 % fix. So after searching all over the internet and speaking with life long Ford mechanics I ran across you tube videos on vapor lock. I found that in the 60's and the 70's that Ford, Dodge, Plymouth and other used a vapor separator in the fuel line just after the mechanical fuel pump. This returns the access fuel and vapor to the fuel tank allowing a Constance flow of fuel preventing over heating of the fuel. These cars came with a return line to the fuel tank from the factory. This is the same as today with fuel injection has return lines to the fuel tank. This all made since to me so I saw a video of a guy drilling a hole in the sending unit and JB welding it in (not sure I wanted to do that) fixed his problem 100%. So I went on the hunt and found the WIX 33041 vapor separator. I also found out the Ford used three different ones. They had .04, .06, and .08 orifices. The Wix 33041 has a .06 orifice in it and was used on 70 chevys. I also read about electric fuel pumps electric fans but this made the more since to me. I found on EBAY a fuel sending unit for 64 - 68 Mustangs with a 1/4 inch return line built in with a check ball only allowing fuel and vapor to return to the tank sold by MCM products. They also sell them on Summit racing but are twice the price. I also ordered 1/4 aluminum fuel line from Speedway racing parts and the filter from O'reilly auto parts.

Fuel sending unit 39.50
Vapor Separator 8.00
Fuel line 15.00
I will be installing this this coming Tuesday when my buddy's lift is free. I have 100% confidence this will be the cure!!

rise66 said:
I installed the Vapor Separator yesterday everything went well, really easy with the aluminum line bending it to match the fuel line. I drove the car reaching operating temperature and continued driving for another 30 minutes with no stalling at stops or sputtering. Turned car off and waited 20 minutes checking for restart problems and listening to the carburetor for fuel boiling. I did not hear any indication that it was, so let's try starting it, fired right up no problem. Next I drove about 30 minutes and stopped to refuel (no ethanol) loosened the gas cap and I could hear the release of pressure so that told me the Vapor separator was operating correctly. Filled the tank went inside to pay and returned. Turned the key and fired right up! So now I will continue driving and look forward to see what happens in 90 degree weather. I due believe I have found the cure!

While rebuilding the carburetor to address vapor lock won't do anything unless there's actually a problem with the carburetor itself, the rest of this is sound advice.

Another recommendation (and what has worked for me on both a Chevy small block and a Ford 302 fighting vapor-lock since the introduction of ethanol-blended fuels) is to sleeve the fuel line in insulation under the hood. https://www.designengineering.com/heat-sheath-aluminized-sleeving/ This stuff works VERY well, and actually looks good doing it.

rbohm · Apr 29, 2020

something else to consider, check the rubber fuel lines to make sure they are not drawing air. i had that very issue on a 79 oldsmobile i once owned. the line out of the tank to the steel hard line in the back would become porus when things warmed up. eventually it would draw air all the time.

rise66 · May 30, 2020

Just an update: I have been driving the Mustang for a month now and no issues problem solved!!

Air in fuel lines or vapor lock?

989153

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Air in fuel lines or vapor lock?

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