Because I HIGHLY doubt anyone would even consider doing it in the middle of combat. If I were about to be shot at, the last thing I would do is turn off my engine in hopes of making the attacker fly by. Even if I were successful in doing it, I would not want to worry about trying to instantly restart the engine 5 seconds later.
Anyone that says they would do it, I challenge to take up a real plane, shut down the engine, pull some sort of crazy maneuver (to simulate avoiding an attacking bandit) and then restart the engine again to continue flying.
Seeing as you fly the Mustang a lot, I am assuming you use this tactic in it as well. Bottom line, there is no way you would shut down a Merlin engine from full RPMs and Manifold pressure and then restart it again at full RPMs and Manifold pressure. No Way, No How.
Aside from blown transmission, busted piston seals, a bent crank shaft, backfiring in the exhaust headers and crushed booster vanes, the entire engine would be flooded out from too rich a fuel mixture. So, even if you hadn't destoryed the engine, it wouldn't start again until you got some more oxygen into the fuel/air mix.
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Here's the ignition sequence for the Mustang... Omit where stating cold engine, as we are obviously talking about restarting hot...
STARTING AND WARM-UP
Ignition switch OFF.
Have prop pulled through if it has been idle more than 2 hours.
Generator and battery switch ON, unless battery cart is being used, then battery switch OFF.
Throttle 1 inch open.
Mixture control in IDLE CUT-OFF.
Propeller control in INCREASED RPM.
Supercharger switch in AUTOMATIC.
Carburetor air control in RAM AIR.
Turn ignition switch to BOTH.
Fuel shut-off valve ON and fuel selector valve to Fuselage tank (if full), or Left Main tank if Fuselage tank not serviced.
Fuel booster pump on NORMAL and check for 8-12 pounds of fuel pressure.
Prime engine 3 to 4 shots when cold. 1 to 2 when warm.
See that prop is clear.
Lift guard on starter switch on pilot's switch panel and press switch to START. Caution in use of starter not to overheat.
As engine starts, move mixture control to AUTO RICH. If engine does not fire, after several turns, continue priming.
WARNING: When engine is not firing, mixture control should be in IDLE CUT-OFF.
Warm engine at approximately 1300 RPM. Check for constant oil pressure. If no oil pressure or low pressure after 30 seconds, shut off engine.
Check all instruments for proper readings.
Check hydraulic system operation by lowering and raising flaps.
Loading 800-850 pounds and unloading at 1050-1100 pounds.
Check communication equipment for proper operation.
Uncage all gyro instruments.
Check both LEFT and RIGHT MAIN and FUSELAGE fuel systems by rotating fuel selector valve with booster pump switch in EMERGENCY. Check for 14-19 lbs/sq. in. If drop tanks are installed, check fuel flow by rotating fuel selector control.
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Here is the shutdown procedure
Booster pump OFF>
Oil and coolant shutters OPEN.
Run engine to 1500 RPM, set mixture control to IDLE CUT-OFF and move throttle fully open.
Turn ignition switch OFF after propeller stops turning.
Fuel shut-off valve OFF.
Turn all switches OFF.
Lock controls.