Loosing fuel prime WC12

[MIKEN]

My WC12 looses fuel prime after siting a day or two. No fuel leaks can be found. I have to take off fuel line at carb and prime the line with fuel to get
the carb to pick up fuel for start. Truck is not equipped with a fuel pump / with hand primer. I do have a NOS Dodge fuel pump with primer, but am afraid
to use it because it has the old style tare like diaphrams. One suggestion given me is that the check valve in fuel pump might be weak and allowing fuel to
seep past. Any thoughts? Mike

[dashtp40]

miken,
I will second the suggestion, it sounds like the pump check valve is leaking. I rebuilt my original pump with a kit from Midwest Military, they supplied a diaphragm compatible with ethanol. Mine leaks down after about a week, but the hand primer is nice to pump the pressure up.
Steve

[June J]

Hi Mike,
the fuel bowl in your carburetor is vented to atmosphere, as are all carb bowls. This means that the gas in your carb will evaporate off over a few days thus leaving the carb empty and as a result you have to put some gas in the fuel line to allow your start up. The problem has nothing to do with the valves in your fuel pump as, because of the vent to atmosphere, the fuel simply cannot siphon out of the carb.

I would strongly advise you to use your NOS fuel pump, but get John Bizal to send you a new diaphragm that is resistant to ethanol and install that before you fit the pump. Put a couple of drops of light oil onto the inlet port of the pump and work the lever. This will moisten the suction valve and help with the initial drawing of gas from the tank.
Once you install the new pump you will be able to hand prime your carb before you start up.

The other alternative is to mount an electric fuel pump on the rear of the chassis and simply turn this on to refill the card for a start up. Once the engine is running your mechanical pump will happily pull gas through it so you can switch it off.

Cheers

Ian

[MIKEN]

Thanks Steve and Ian. I am going to look into a rebuild on the NOS pump with primer.
Mike

[Gordon_M]

Any original fuel hose could cause that.

They go spongey to the point that fuel wont leak out, but air can leak in, so if you have a hose in a position to draw air into the system it will pretty much all return to the lowest point.

Just change out any original braded fuel hoses to something that will withstand modern fuel.

The firewall-mounted filter with hoses on the 3/4 ton is particularly prone to this.