Need help with my chevelle

[ClassicCar.com]

I have a 1972 Chevelle and Iv been having a problem with it. When ever I park it on a hill and leave it there for over an hour or so it will not start, i then have to prime the carb to get it started again, What could be causeing this? If it help I had replaced the old carter with an edelbrock carb, I dont know if this may have contributed to the problem.

[ClassicCar.com]

Annon, How steep is this hill? I can think of three things off the top of my head. You float bowle syphoning back, The carb is leaking at the float bowle cover due to the angle of the park, Lastly due to the angle of the float bowle you are not generating eouph vacume do draw the fuel into the throat of the carb.