What will cause my float bowls to go dry

OK Here is what I'm running. It is a Holley #4150 (750) and it was rebuilt with the Quick Fuel Tech. billet metering blocks on both sides.
Here's the problem. When the car sits for a few days both of the bowls are dry. Even the pump is dry.
And here's another thing. If you let the car sit for a half hour and then restart it, it just runs really poor. It seems like its really rich.
If you have had this problem please let me know.
Thank you...............Ted