Fuel line check valve?
 

After turning off my '54 Mercury with mechanical fuel pump, gas slowing drains out of the glass bowl until it reaches the top level of the inlet port. Its an AC 4052 dual action pump - gas and vacuum. Is there supposed to be a check valve somewhere in the fuel supply line? I am running just a short length of rubber fuel line from the rigid line to the pump.

Re: Fuel line check valve?
 

How long does it take to drain down?

I believe the outlet valve in the fuel pump 'should' prevent this from happening. If there isn't a filter before the fuel pump it may have a small bit of debris stuck in it???

Re: Fuel line check valve?
 

It takes less than a minute to drain down. The 2 check valves inside the fuel pump affect the gas inside the diaphragm chamber within the pump. In my case, gas is draining from the glass bowl back into the supply line, before the gas spills down the center column into the diaphragm chamber.

Re: Fuel line check valve?
 

You may have a restriction in your vent line on the tank resulting in a vacuum condition which sucks the fuel back to tank. Try removing the gas cap as soon as you shut car off and see if it goes down then.

Re: Fuel line check valve?
 

JMFL36, Is your photo in the first post upside down, or right-side up?

If the inlet & outlet valves in the pump aren't sealing as well as they should the fuel in the filter and line up to the carburetor can drain down to something like the level of fuel in the tank.

If you get a whoosh of air moving into or out of the gas tank when you take the gas cap off, the tank vent isn't working. If there isn't a separate outside vent line, the vent may be a very small opening in the gas cap.
.

Re: Fuel line check valve?
 

'54 Mercury's were different than other Y-Block fuel pumps. They have the glass bowl/filter on top, and the vacuum pump on the bottom.
I've seen the fuel in the bowl low before, but wasn't an issue in how the car ran. If it starts and runs good, I would say good enough.

Sal

Re: Fuel line check valve?
 

Took CrownVic55's advice and loosened the non-vented gas cap, started the car, ran it for a bit, and shut it off. Bowl stayed full. I must have a restriction in the gas tank vent line. I'll throw it on the lift tomorrow and blow out the vent line. Will let everyone know how it goes.

Re: Fuel line check valve?
 

If the 54 Merc's tans are the same as my 54 Ford, there is no vent line. 54's used a vented cap - that seems to be the problem. Just drill a 1/16 hole in the cap.

Re: Fuel line check valve?
 

The 54 MERC was externally vented and had a closed filler cap.

Re: Fuel line check valve?
 

Looking at the diagram... does the 'top' end of the vent line connect into the upper part of the filler neck, or is it open to outside air with some sort of small fitting on it?
.

Re: Fuel line check valve?
 

On my 55 Crown the vent line exits the body close beside the filler neck. Open to outside air. If car has sit for awhile, it may have spider web or dead insects in it.

Re: Fuel line check valve?
 

Ain't this something?

THE MERC shows the vent above the fuel filler in the rear body panel. The MPC shows the 55/56 FORD sedan vent tied into the tank filler tube. Both vehicles show non-vented filler cap.

Earlier thread on same vehicle - https://www.fordbarn.com/forum/showthread.php?t=294148

I bet them mud-dawbers love that vent opening ... :p

Re: Fuel line check valve?
 

Finally got to work on the Mercury today. I traced the fuel line from the tank to the fuel pump and found a spot where the steel fuel line comes within an inch of the exhaust pipe. (My '54 has dual exhaust so does not have the front crossover pipe like most Ford and Mercury cars of that year.)

After the car heats up the steel fuel line gets very hot in this spot and boils the gas before it gets to the fuel pump. This causes the sediment bowl to fill up with bubbles and eventually starve the pump (and car) of fuel.

Today I encased the fuel line in that area with a length of DEI Heat Shield Sleeve and wrapped the exhaust pipe there with some DEI Heat Shield Wrap. See the photo for details.

I drove the car, stopping a few times to check the sediment bowl for bubbles. None. Fingers crossed, problem solved.

Re: Fuel line check valve?
 

The work looks very nice but how close they are to each other makes me nervous.
If there's a way to relocate that fuel line farther away it could be an excellent idea.
Don't want to hear about you on the news for a bad reason.
.

Re: Fuel line check valve?
 

Yeah, I'm going to see if I can bend the fuel line to get a few inches clearance between it and the exhaust. The line is a new pre-bent stainless line from Classic Tube, but I'm guessing the factory must have rerouted the line in that area for optional dual exhaust cars.

Re: Fuel line check valve?
 

Regardless, good diagnostic skill ...

Re: Fuel line check valve?
 

Yeah, I probably could have added this to that other thread but it turned out there were two separate problems I was fighting - a blocked vent tube (previous thread) and vapor lock (this thread). So hopefully the separate threads will help others find what they're looking for. Thanks again to everyone for all the good advice.