1971 Johnson 4HP Outboard Motors Service Manual, Page 26Get this manual
DESCRIPTION MAGNETO ignition system consists of flywheel type magneto connected to the spark plugs through high tension leadsmagneto is self-contained electrical generating unit consisting of an armature plate with two ignition and lamination assemblies, condensers, and breaker assembliespermanent magnet cast into the flywheel completes the assembly
OF OPERATION
magneto employs the interaction of the fast moving flywheel magnet and stationary to generate an electric current of voltage sufficient to across the spark plug air gapThis creates the spark that ignites the fuel in the cylinderignition actually consists of two coilsOne, called the primary, consists of relatively few turns of heavy gage wireThe other, called the secondary, consists of many turns of fine gage wirecoils separated insulation and mounted the center leg of an shaped laminated iron One end of both the primary and secondary coils is grounded to the other end of the primary connects to the insulated stationary breaker pointother end of the secondary coil connects to the spark plugcoil and movable breaker point grounded to the armature plateSECONDARY WINDING