odd fuel problem

Two months ago the fuel pump went on the F-134 in my FC-150. So I replaced it. Now when it sits over night it won't start, just cranks and cranks. Everything else is good, plugs, points, wires, cap and rotor. Good spark. In order to get it to start I have to loosen the fuel line at the carburetor, it is a single barrel Weber, until some fuel bleeds out than it starts right up and runs fine. I discovered this by accident while checking to make sure I was getting fuel at the carburetor. Fortunately, on a 150 the fuel line is just under a small door in the engine cover next to the driver's seat. I just keep the right size metal fitting wrench next to the driver's seat. I can't figure out what could cause this problem.
Thanks

 

I'm just guessing but it sounds like the fuel pump is loosing prime? Can that even happen?

 

sounds like a crack in the fuel line somewhere,pull fuel line off carb and crank see if you get a steady shot , (don't smoke while trying this). or maybe the bowl is drained dry and leaking out somehow, is it possible to pull the top off the carb before it starts to see if there is still fuel in the bowl?

 

aallison, Fuel pumps can lose their prime. The valve in the pump allows gas to flow to the carb but not back wards. It can be damaged or just leaking. The pump that I replaced was old enough to have screws holding the diaphragm chamber together. Several years ago I had another no start but got spark situation. No fuel was flowing to the carb when I removed the line and cranked it over. When I disassembled the fuel pump one of the round metal parts that holds the rubber diaphragm had fallen out of its holder. Apparently it is only staked in place at manufacture. I re staked it and it ran for another two years.
cjs/442, I will take the fuel line off before I try to crank it and see if I have fuel.
Thanks for the replies.