Thank you, I was laughing as I wrote it. In the 1970's , run-on was common. That is why the solenoids were on the throttle linkage. Your idle was adjusted on the solenoid. When the key was off, the plunger retracted, the throttle absolutely closed and allowed no fuel to flow in the idle circuit. No fuel = no run-on. Now, with the key off and NO solenoid, the engine heat allowed the engine to keep detonating the fuel. The engine rotation obviously kept the idle fuel flowing because the engine is a vacuum pump and rotation sucked more fuel in until the heat subsided enough to end the situation. The backward rotation happened when the detonation occurred on the slow rotation of a dying engine and the piston could not go over top dead center and kicked backward. This reverse rotation had a high rpm due to the lack of compression resistance, so the engine did this amazing reverse blast on the last bit of fuel and then partially burned exhaust gasses were backing up into the combustion chamber, and backing through the intake manifold, carburetor and air cleaner and scaring people who heard the noise and saw the smoke.
