Is the fuel tank properly vented??? This is what Pat was alluding to in his post above. Sometimes as fuel is drained from the tank, a vaccum forms that prevents the flow of fueln from the tank tot he carburetor. Therefore, try running the car without the fuel cap installed and see if the probelm persists. If the problem away, then you need a vented fuel cap. If the problem persists, then you have eliminated one possiblity and we'll move on from there.

Paul