Car is my Dad's '73 Swinger, 318 auto with A/C, PS, PB. It has an Edelbrock Intake and carb, otherwise it is stock.

The car starts and runs great when cool, but once it's been on the road for awhile, it doesn't want to idle in gear and has to be turned over for awhile and pumped hard to start. It doesn't have to sit for the hard start issue to be a problem. It can kill at a stop sign and the starter chugs away for awhile before the engine finally fires.

The car sits 8-9 months out of the year.

Any help on where to start troubleshooting would be much appreciated.

Have you tried adjusting the air fuel mixture screws and the idle speed?

Dad adjusted the idle, but I don't think he's changed the mix at all.

E10 (ethanol) gas will cause that. A thick ~3/8" Felpro gasket between manifold & carb will likely help some. Might shoot a 2 second blast of starting fluid into each of the idle mixture screw ports on the carb base to clean out the idle circuit. Need to afix one of those thin red straws to the nozzle on a can of starting fluid to get a good shot in there right in the port.