I had this happen on my old 63 Nova with either an Edelbrock or Demon carb. The problem seemed to be the Edelbrock fuel pump. I don't think there's any anti-drainback valve in it. I never did check into the possbility of installing a valve like that between the tank and the pump, but it seems like it otta work. I don't know of any sources for such a valve, tho.
