Originally Posted by
hugh flung_dung
It takes an almost constant time for the flame front to propagate so if the engine is turning slowly the spark needs to occur later than when it's turning fast. One mag has an impulse coupling which delays the ignition timing at cranking RPM.
HFD
Some of us have replaced the old Bendix mags with Slick. They don't have an impulse mag, so both should be on. Moreover, we also have replaced the old starter motor with a modern Sky-Tec which spins the engine very much faster so spat can occur earlier.