Fuel Problems????

I have a 70 383 all rebuilt, new carb,fuel lines and sender. When I crank it up the filter fills up with fuel but after a day are two it will drain out of the filter. This isn't perking out it is just starting for and letting it fill the filter up. Does the fuel pump have a valve to stop this are they made where they'll drain back? It is a brand new pump. Has any one else run into this? Ronnie