First thing to check would be the Choke circuit, when cold - is the choke blade closing when you step all the way down on the pedal first time?
(hopefully most realize on older choke equiped cars, you need to 'Set' the choke system by stepping all the way down on the throttle once before
trying to crank the starter ...)
Next, is the fuel bowl retaining fuel after long periods of no-use.
Rochester Q-Jets had a bad habit of the main fuel jet plugs in the base of the fuel bowl coming loose or the seal cracking and they'd leak the fuel out of the bowl over a period of time.
The 'fix' is to epoxy the plugs back in place. This requires removal of the carb. and taking the bottom throttle plate off to gain access to them.
Here's a bowl that has had the plugs epoxied -
If none of above are the problem, here are a couple other items to check;
1.) Does the fuel pump have a bad 'check-valve' - allowing the fuel to drain back to tank level?
2.) Along with above - the correct carb. inlet fuel filter should have an "Anti-drainback" Check valve built into the rubber seal on the end - GM released these modified fitlers in the 70's to combat the drain back issues.
3.) Has the accelerator pump seal (often called the 'Umbrella') shrunk up over the years and is preventing a good pump shot for starting? (note: this can be more common if the carb has sat around for a time drained or if the fuel bowls are leaking-down and the car sits for long periods, this tends to dry-out the seal.)
Hope this helps