Carb Fuel Evaporation?

I ran a stock 68 AVS on my 340 in my 65 and that thing would not hold gas for more than about a day. Not sure what was up but I put in a carter electric pump and every morning Id turn the pump on manually with a switch under the dash and it would pump for about 5 seconds ans then slow down to almost nothing. Motor would start instantly every time. If I didnt run the pump, the car would start (maybe) but would be very lean and would die after about 10 seconds. Forgot a few times and started to sputter on the street until I flipped the switch and off I went. Good theft deterent too. The Facet jigglers are just one way check valves on a little magnetic shuttle going back and forth. The way they are designed is they allow fuel to flow through them but not back. The forward motion of the shuttle would compress the fuel in the line to the carb and on the way back will pick up more fuel. They were self regulating 1.5-3 psi if there was enough pressure in the carb side, the electromagnet force would not be strong enough to cycle it forward and it would just sort of vibrate.