Looks like you have bad needle and seat. The rubber in the assembly is probably dried out and disintigrating.
I had those exact symptoms on my Holley 500 cfm. Turned out to be the needle and seat.
I changed it and did a complete rebuild. Now, I don't even have to pump the gas when starting in the morning. Bump the key, hands free, starts right over. Also after a long run I let it sit 5 minutes, bump the starter fires right up. No pumping the gas. Let it sit 30 min, hour, two hours, 6 hours , etc; bump the key start without pumping the gas, starts right up.