When the car is warmed up after running, the carb does squirt gas. But left over night, the gas flows back away from the carb.

 

I could be wrong, but if it were my car, I would put a new fuel pump on it. They're not that expensive for a stock replacement. I would assume that maybe the fuel pump is starting to go and won't hold enough pressure to keep the gas up to the carb. I had one that would do the same and also had one with a bad accelerator pump and it would still start without gas poured down the carb. Just a thought...

 

i'd say your problem is as simple as the carb loosing all fuel over night
as you said draining back is somethign I've seen before, but the fuel bowls should not be empty.
whatever is in the bowls should stay there. overnight as well.
I would forget about the fuel pump for the moment. You need to check where the petrol is going.

Since you say the carb sprays when you move throttle the accellerator pump is ok. I just assume the bowls are empty in the morning.
There's only two reasons for that I could think off:
- leak (outside or inside the carb)
- carb getting too hot after switch off causing the fuel to evaporate

There's two tests you could do:
a) get your car started and as soon as it is started don't let it warm up. switch off. come back after the night and see if it squirts. If it doesn't I would say it's not heat related
b) if you take off the top of the carb in the morning check if there's actually any fuel in there. and if there is how much.

To remove the top on an edelbrock is very very easy
Remove all the linkage at the top of carb (it's only 2 or 3). all c-clips or cotter pins.
In my 1806 there was two torx screws next to the airhorn with a little metal plate that would hold the springs and metering rods. loosen them, move metal tab to the side and pull the metring rods and springs out
then open all the other torx screws and remove the top.
putting it back is reverse order.
Check the manuals if unsure. they are very good. very detailed

Kalli