Stopping an engine with ICO assures that no fuel is left to burn as the engine slows to a stop. If there are glowing deposits in the cylinders, and you have shut down by turning the mags off, the continued flow of fuel into the combustion chambers can be ignited by the glowing deposits, and cause a backfire.
Glowing deposits? And how did they get there??? Are you suggesting a good source of pre-ignition or the theoretical and hard to replicate highly carboned up due to poor mixture abuse situation? And I often shut big pistons down with the mags. Never been a problem.
If the engine is in fine order, it should stop!
Otherwise, I would like to see hard data on these.
and cause a backfire. Such backfire or run on can be unsafe, when you simply want the propeller to stop, and can be damaging to the exhaust, if that is where it occurs.
A Backfire is when a flame front goes back through the carby, and not easily achieved. Not normally followed by any run on. A run on is usually from a faulty ICO. So which is it? Not likely to have both.
To a lesser degree, the now flooded engine can be more difficult to restart, if you want to do that right away.
Flooded? how so? you pumped the primer? Run the boost pump at WOT/Full Rich?
I too have flown aircraft which had to be shut off with the mags, for lack of a mixture control, in which case you obviously have no choice.
I have had .... i forget now, 700-800 hours on these types, LOTS of starts and stops, thousands, and not once have I had an instant restart problem, they start in 180 degrees, nor any backfire, after fire or anything. In fact hot or cold they were the easiest to start.
Less OWT's and more science please.
