Dieseling, afterrunning, scares many drivers.
"Dieseling" in a spark ignition engine is a term used to describe a run-on condition which occurs after the ignition is turned off. It can be caused by a number of things, but your initial timing setting is not one of them. "Dieseling" occurs when the ignition is off, and therefore no spark is present.
For "Dieseling" to occur, you need the presence of air and fuel, as well as a source of ignition. In carbureted engines, an air/fuel mixture can continue to enter the engine during the coast down of the engine after the ignition is turned off. The engine continues to pull air thru the carburetor, and the carburetor contines to mix fuel with it. This can be aggravated by a high idle setting; more air/fuel is delivered. The source of ignition can be a "hot spot" in the combustion chamber, which remains hot enough after the ignition is turned off to initiate combustion. This can be a carbon deposit, sharp edge, or even the spark plug electrode itself.
Modern fuel injected engines are not plagued with "Dieseling", as the fuel AND ignition are turned off when the engine is stopped.
Some early emissions controlled carbureted engines exhibited "Dieseling", even when new. To control this condition, these engines used a solenoid operated idle throttle position control which permitted the throttle to be held in a more open position to provide sufficient idle speed, but closed completely when the ignition was turned off to prevent "Dieseling".
You need to focus on the causes: Too much air/fuel after ignition shut-off, the "hot spot" (source of ignition", or both.
Also when the cylinder creates its own combution heat...without the need for a spark. It's a combination of timing, running hotter than engine design intended (for emissions reduction) and higher compression. A normal internal combustion engine doesn't have enough compression to ignite the fuel charge only with compression heating effect. But, throw the other conditions into the mix, and it can (and does) happen with the ICE. GM used a lot of 'tricks' to prevent this, such as:shutting the air supply off completely, turning on the A/C compressor when the engine is cut off so that it will load it enough to stop, etc.
If you have a hi-compression engine with the emissions stuff still intact, you will have to get 'creative', too. Back in the day, most of us just put the car in gear when we turned the engine off (released clutch a bit after engine "off"). That would 'kill' the engine with no problem.