Check Valve in fuel line

[BobsMK4]

After sitting for a week or more, my MK4 takes over 5 long cranks to start. I have a 302 crate motor with a Eldebrock 650 carburetor. The fuel must be draining back into the tank. It takes the mechanical fuel pump a while to pump fuel back into the carburetor. In order to stop the fuel from draining back to the tank, I plan to install a check valve somewhere in the fuel line. Has anybody installed a check valve in the fuel line to make starting easier? If so, what check valve did you use and where in the fuel line did you install it? I would rather try this first over installing a low pressure electric fuel pump. Any help with this problem would be appreciated.

[NAZ]

I've used check valves on fuel systems to prevent drain back and placed them on the suction side of the diaphragm pump and close to it. If you use a spring loaded poppet style check you can mount them in any orientation. If you use a gravity check it must be mounted so that gravity pulls the check to the closed position.

I also use Oberg spring checks on race car fuel cells to prevent fuel loss in the event of a crash that rips the fuel hose off. https://www.obergfilters.com/product/fuel-safety-check-valve/ I like to mount them submerged in the fuel cell on the pick up tube but have also mounted them on the supply and return lines external and directly on the cell connections. The spring in these checks are weak enough the suction from the fuel pump will open it and when the pump shuts off they instantly close, preventing fuel from leaking out of the fuel cell even if the hose has been ripped off. It also prevents drain back so when the pump starts, pressure builds instantly.

Look at Summit Racing for a selection of fuel line check valves. For your application I'd suggest you mount it on the suction side of the pump as close to the pump as practical.

[CraigS]

Are the float bowls empty? If they are still close to full, gas draining to the tank won't matter. The carb will have enough gas to run the engine until the pump catches up. 15 years of running a 351/408 w/ a carb and mechanical pump and I never had this problem. It is not impossible but I think it is very unlikely you need a 1 way valve.

[rich grsc]

The mechanical pump is a one way valve, you don't need a second one. If the fuel is draining back to the tank, then the pump is bad. Check your oil to see if it smells like fuel, a hole in a diaphragm can leak fuel into the crankcase.

[Railroad]

Not to insult anyone, but starting a cold carb car is different than a fuel injected one.
Does your carb have or use the choke, are you giving the gas pedal a couple of pumps before starting?

[BobsMK4]

Not to insult anyone, but starting a cold carb car is different than a fuel injected one.
Does your carb have or use the choke, are you giving the gas pedal a couple of pumps before starting?

My carb does have a choke. I turn the key to the on position and press the gas pedal to the floor to set the choke and then I pump the gas pedal a couple of times. This works fine if started within a week of the last start. After 2 to 3 weeks is when it takes several tries in order to start. Otherwise, the engine runs great with no hesitation at all.

[BobsMK4]

I don’t think the mechanical fuel pump is bad. There is no smell of fuel in the oil.

[BobsMK4]

The mechanical pump is a one way valve, you don't need a second one. If the fuel is draining back to the tank, then the pump is bad. Check your oil to see if it smells like fuel, a hole in a diaphragm can leak fuel into the crankcase.

Well how do you explain the hard starting after sitting for a couple of weeks?

[rich grsc]

Well how do you explain the hard starting after sitting for a couple of weeks?
I'm not sure, doesn't seem to make much sense, but the diaphragm in the pump could be bad, and NOT leak into the oil.

[Railroad]

I do not recall hearing of a bowl leaking issue with the Edel carbs. It sounds like the gasoline in the carb bowl is gone when you encounter the long cranking issue. Is your car stored in an unusually hot area? Are you seeing any gasoline stains on the intake around the carb? Did you do any internal work on the carb? Maybe your carb fuel level is low and the amount of gasoline to evaporate is less than it should be.
You can fill the carb before starting, through the vent holes on the carb. Try starting after adding gas to the carb and see what the results are.
You can pinch off the fuel line when stored, to prevent any siphoning. I do not think the fuel lines can siphon back through the needle and seat.
good luck,

[OVCobra]

I am doubtful that the fuel pump is allowing fuel to siphon back to the tank as it has two check valves in it to operate. Similarly I doubt it would siphon from the carb past the inlet needle/float.
While I have no experience with Edelbrock/Carter AFB carbs, I understand that they can have problems with fuel siphoning through the boosters (into the intake) if/when the air bleeds get dirty/plugged. Apparently it can lower the fuel level (in the carb) enough to starve the accelerator pump thus hard starting? Found it on this link https://www.jalopyjournal.com/forum/threads/edelbrock-afb-leaking-fuel-in-intake.1189549/

Good luck

[Ian G]

Unless there is an external leak, I don't see how the fuel can drain from that carb. The Edelbrock is a clone of the old Carter AVS. The floats and needle valves are in the lid and will not syphon backwards. With that time frame there could be an evaporation problem. I would make sure the choke is closing properly, but if you pump the gas pedal enough it should still start.

[Railroad]

I wonder if the carb fuel is perking out due to heat. Might make sure the fuel lines are not cooking before going into the carb and the carb has enough gasket to insulate the carb.

[tonywy]

I had the same issue with the Edelbrock carb. When left sit for a week or longer it had a long crank time to bring fuel up. I had attributed that to evaporation. I have switched to a custom built modified Holley double pumper/no choke. No more issues.