It's the fuel evaporating in the fuel bowls.
Now you have no accelerator pump shot and now it won't easily start.

For some reason, some engines do not need pump shot to start, these engines don't mind having and Edelbrock on them.

Why does it take so much cranking before you have pump shot? First the passenger side fuel bowl needs to be full. Once it's full fuel will then flow over to the driver's side fuel bowl. Once it's full it's high enough to feed the acc pump cylinder. Then without a constant supply it will only give you a couple of pump shots, hopefully it's enough to fire up your cold engine.

Guess why Holley's do NOT have this problem?

Even with 80% of their fuel bowl contents evaporated. Since it's acc pump feeds from the bottom, it'll squirt as much as you desire and that cold, not started in 2 months engine will instantly spark to life.