Slight "Dieseling" or "Run on"

Lean mixture/vacuum leak, improper ignition timing, restricted exhaust, carboned-up combustion chambers and/or spark plugs, improper spark plugs, proper spark plugs but someone forgot to remove the metal ring washers from them before installing them so they're overheating, severely crudded-up cylinder head coolant passages, improper idle speed, improper cam timing…

What's the status of the car's EGR system?

Tune-up parts and technique suggestions in this thread. Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download.