I have a 66 with a mild 351w. sometimes when shutting off the car, the motor still wants to stay on but then slowly shuts off. doesnt sound to good either. what can this mean?
A few different things can casue this...at least from the sound of it you are talking about "dieseling" or "run on". A vacuum leack, carb too rich or too lean, or carbon build up in the engine are some of the more comon causes. How many miles does the engine have on it?
That's pretty low to be a carbon issue, I would check for vacuum leaks first, then make sure that the choke is not hanging up. How good are you mechanically? Not a shot, just a question. If you are pretty good, you can true the "water fix"...if it IS carbon somehow, run the engine at fast idle and SLOWLY pour water down the carb...the water will break up the carbon. BUT if you pour too fast you will damage the engine, so if you are not comfortable with that, DON'T do it.
You can try turning off your car with it in gear, then put it in park after it turns off. It will keep the engine from turning over. I think a high float level can also make the dieseling worse too.