Hot Restart Problem

The 318 in my son's '68 Dart has an intermittent hot restart issue. After sitting for 5-10 minutes, sometimes it will cough back through the carb, and then crank for 10-15 seconds before starting. Most of the time its turn the key, squeeze the gas and vroom it starts. Never does this when cold, hot only, and only intermittently. The car runs and drives fine, just has this hot restart issue. Engine stats are: rebuilt stock 318 with 600 Holley with 68 primaries, Edelbrock Performer intake, HEI ignition upgrade, 18 degrees base timing. Anyone have any thoughts on this..?? Could this be a sticking intake valve...?