Carb Fuel Evaporation?

Sometimes I don't drive my Dart for a month, when I go out to start it, I let it turn over for 8 seconds without touching the gas pedal, let it set for a couple of seconds and do it again, then I pump it 2 or 3 times and it starts right up, I have to mess with the gas pedal to keep it running. I have a 340 with a Edelbrock 800 AVS2 and their insulator gasket. No choke.