as the ignition is triggered it sends the spark through the rotor, to the cap, down the wire and then it jumps the gap of the spark plug. a spark kernel is created that ignites the air/fuel mixture in the combustion chamber. Proper timing of this spark is not the only concern, you must have the proper heat range as well as the correct gap.
thats how i think one works.
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TR "Old Skool EF" Member #121(aka#420)