Carter 2 barrell on 383

Having a problem with my "C" bodies 383. It has a new fuel pump and glass fuel filter. Original Carter 2 barrell. Problem is after the car sits for about 30 minutes there is no fuel visible in the fuel filter and the car will not start without pouring a little bit of fuel down the carb. Once it is started the fuel fills the filter and the car runs fine. The carb has never been rebuilt to my knowledge. I am planning on sending it to Carb-X next week. Ant ideas on what could be causing this problem?