Carb losing prime

[oldmountainfarm]

I have a 72 Mach 1 with a 351 C 4V. The carb keeps losing prime. I've put new fuel line from front to back, new mechanical fuel pump, new gas tank, New carb, and even put an electric fuel pump right at the tank. I can pour gas down the carb and eventually get it to run and it runs great. Cut it off and the next day there is no gas in the line. As far as I can tell, it's not leaking gas anywhere.

 

[CZ-75]

If it's not leaking, and there is no gas in the line, then it sounds like the gas is traveling back downhill toward the tank...

Maybe put a check valve in the line close to the electric pump, but on the carb side?

 

[caspianwendell]

sounds like the vent is stopped up and creating a vacuum in the tank

 

[oldmountainfarm]

I will check the vent this weekend. I've been restoring it for the past couple of years and it seems everywhere a dirt dobber can get in and make a nest, they have been. Can't see putting a check valve in although that it a good idea. I would rather fix the problem.

 

[MotoArts]

What kind of carb?

 

[72HCODE]

you could try this as an experiment for 24 hours.

remove the gas cap or twist the cap so it is open but still on the car. then start the engine prime the carb, shutdown and let sit for 24 hours come back and check the lines again if

they are not empty like before then i would suspect the gas tank vent is clogged up and a vaccum is forming inside the tank sucking the fuel back through the lines on shutdown.

fast solution is buy a 1970 vented gas cap and just keep going until rebuild time.

if the lines are still draining down or maybe its the carb fuel bowl just draining you may have a crack and its leaking into the intake.

 

[oldmountainfarm]

It's a new Holley I just put on this week. The carb I just replaced was a Holley my wife rebuilt. I don't think it's the carb. I took the gas cap off last night and started it and I'm going out there in a little while and check the lines.

 

[73vertproject]

The carb I just replaced was a Holley my wife rebuilt.

You are one lucky guy! :salute:

 

[oldmountainfarm]

I don't know about that Doc, she's a diehard Chevrolet woman.

 

[oldmountainfarm]

Ended up being the mechanical fuel pump, which was new. Took it off and just used the electric fuel pump with a pressure regulator and it has fired up ever since.

 

[73vertproject]

Glad to hear you got it worked out. Thanks for posting and letting us know!

 

[VegasFastback]

Ended up being the mechanical fuel pump, which was new. Took it off and just used the electric fuel pump with a pressure regulator and it has fired up ever since.

Man those thing are cheap they're almost as bad as ignition coils.

 

[dlthomps]

Ended up being the mechanical fuel pump, which was new. Took it off and just used the electric fuel pump with a pressure regulator and it has fired up ever since.

Can you provide some information on the electric fuel pump. I'm having a simmilar problem and I'm considering an electric fuel pump. Where did you mount it, what type ect....

 

[JimNiki]

Asking my wife to rebuild my carby is like asking a blind man to thread a needle! Clueless come to mind....