I admit I did NOT read all the posts but hope I can add to the discussion.
The antifire solenoid mounted in the carburetor stops fuel flow thru the main jet, it does not stop flow to the carburetor the needle and seat do that.
If an inline fuel shut off is used whether manual or electric, the engne will not stop until the carburetor is empty, this may also result in engine run on, unless the ignition is killed 1st.
With the carburetor mounted antifire solenoid. the manufactures recommend to shut the engine down at 3/4 to full throttle. Why? as the engine winds down mainly air is pumped thru the engine and into the muffler. This is supposed to pump the fuel out of the muffler so you dong get that BANG. Even if the ignition kills the spark, which should be killed when the switch is shut off.
From the Kohler command opperators manual:
Stopping
1. Remove the load by disengaging all PTO driven
attachments.
2. For Carbureted Engines Without A Shutdown
Solenoid: Move the throttle to the slow or low
idle position. Allow the engine to run at idle for
30-60 seconds; then stop the engine.
For Carbureted Engines Equipped With A
Shutdown Solenoid: Position the throttle control
somewhere between half and full throttle; then
stop the engine.
For EFI Engines: Move the throttle to the slow or
idle position; turn key off to stop engine.