starts great cold, turns over alot when warm...please help!!

[Ramredneck]

I have a 1977 GMC K20, 305, 4 bbl. New starter, solenoid and carb. When it sits for a few days, i give it a pump or two - turn key and starts up great.

After its warm and shut it down for 20-60 minutes or so, it will crank crank crank crank (whether I pump it or not)...i get it to finally start at a low RPM (usually while fluttering the gas pedal).

What does this sound like, I don't really know where to pin point - please help.