Engine Engine Dieseling When Turned Off

As mentioned... we need more information on the setup before any suggestions can be made. Sounds like a high compression, high lift cam motor...

Why would you put 93 in a motor that you were told required 100?

so, let me see if I understand correctly, you shut the car off and it continues to run?

I don't really think timing would have much to contribute on it's own. regardless, you should retard the timing a bit if you're going that big of a jump in fuel. but, when I hear dieseling in gasser engines, my first thought is carbon build up on either/both the pistons and the valves. and the timing advanced timing combined with the lower octane fuel isn't helping. more like exacerbating the issue. you could try over fueling it by a little bit. the fresh fuel will help to cool off the cylinder temperature. that'll help with pre-ignition/detonation/spark knok. with the cooler cylinder temps. that should help with either reducing the run on or eliminate it. down side with a carb is that it's SUPER easy to foul out your spark plugs.

but to be honest, I would recommend going down to your local dodge/jeep/chrysler dealer, going into parts, and getting some decarbonizer. run that through your engine. it should help with the run on.