69 340 AVS fuel leak

I have to agree with RamCharger. I've had this problem several times over the years with factory as well as aftermarket Carter/Edelbrock AFB's. It's the heat from the exhaust X-over passage under the carb flange boiling the fuel in the bowls. Feel the carb when its perc'ing the fuel and I think you'll find the carb is very hot to the touch. Try running a heat-sink/thick carb gasket or plywood-type spacer under the carb,and see if that helps. To solve the problem in the past, I have blocked the exhaust X-over on several engines ,with this problem ,and it has cured it completely.