Fuel trouble in 70 Mustang Mach 1
 

I have a 1970 Mach 1 with a 351C 2V. I was in the process of putting a 1" spacer under the carburetor for more down draft. I put the towels (as I normally have to do) under the carburetor where I normally disconnect the fuel line. I pulled off the fuel line real slow and to my surprise there was no fuel there at all. I had no fuel in the line, in the carburetor, anywhere. It's never done that to me before. I just ran the car a few days before that and it was running fine but it's always been really hard to start. So I need to know, is there a check valve in the fuel pump, fuel line, or fuel filter? Does anyone know where a check ball is or even if there is one? I never heard of it before. Any help, I would appreciate. Thanks!

The 'power valve' on the bottom/underside of the float bowl used to like to crack the diaphram with age and the contents of the fuel bowl would then leak down into the intake manifold.. Usually noticed after sitting over night (or a shorter time depending on the leak) the engine will tend to flood and will/may need some extended cranking to not only clear out the excess fuel, but to refill the bowl as well.. The gas/pressure in the fuel line can run into the float bowl as it bleeds out when the float/arm drops and opens the float valve from the loss of fuel then drains out as well..