Carb Question

You've had some justifiable guesses so far, but run-on (or "dieseling") has many causes -- yes, including improper idle adjustment and overly-advanced timing, among others -- so in order to help you narrow in on what's causing it in your car, we need more info. What's your basic timing set at? What spark plugs are you running? What's your engine idle speed? Any modifications or recent work done on your car? Is yours a California-emissions car, originally?

You may not know the answers to some of these questions, so to avoid wasted time, 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. And you'll want to get the three books described in this thread as soon as you can.