Only thing to add is there should be some fuel in bowl when first starting.
It should not need the fuel pump to run to refill it. There should be enough fuel in the bowl to start and run it for a minute or so.

Quick check: Remove air cleaner lid and see if the accelerator pump shoots fuel out.
If yes. Do it again to see if there's enough fuel in bowl to refill the pump.
If no. remove top of carb to see if there is fuel in the bowl.
If yes, accel pump may need new seal or check valve.
If no, its either weeping out or evaporating.

Also, just know there's several service bulletins in 70s addressing the issues of starting. Some models got an internal bypass in the pump which helped hot starting but made cold starting more difficult.
http://www.imperialclub.org/Repair/Lit/Master/307/index.htm