Carter AVS on a 340 drains of fuel

My 69 Swinger 340 used to do the exact same thing way back in the day. But it didn't happen right away. Mine would take at least over night or if I didn't drive the car for a couple of days then I would have to crank a while to fill the bowls up to get it started. I had a couple of friends and their Darts did the same thing. The only thing I found was that on occasion if it was really hot out and the car was running a little warmer than usual, the carb would take up heat after I shut the car off and the gas would expand and run over the air horns into the intake. Also the vent on the top of the carb for the accelerator pump was open somewhat by design and this allowed for a little evaporation also. I know that it wasn't siphoning though. I clamped off the fuel hose at the filter once for a day to see if it would make a difference and it didn't. The gas simply was evaporating or boiling over. That was the only thing I ever found to be a possibilty.