I used to have an old Petter Stationary engine, with a BTH Impulse Magneto which was timed for a spark at tdc. It would start from zero speed, just pull the flywheel slowly over compression, and 'Bump' the thing would start.
Most Magneto GA aircraft retard the Impulse ignition below slow idle speed to tdc. So as long as the engine doesn't leak it's compression, it might just start if the prop is pulled slowly over tdc compression.
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