1972 Johnson 4HP Outboard Motor Service Manual, Page 26Get this manual
DESCRIPTION MAGNETO The ignition system consists of flywheel type magneto connected to the spark plugs through high tension leadsThe magneto 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
THEORV OF OPERATION
The magneto employs the interaction of the fast ing flywheel magnet and stationary to generate an electric current voltage sufficient to arc across the spark plug air gapThis creates the spark that ignites the fuel in the cylinder Each ignition actually consists two coilsOne, called the primary, consists relatively few turns heavy gage copper wire The other, called the secondary, consists of many turns of fine gage wireThe coils are separated insulation and mounted the center leg of an shaped laminated iron coreOne end both the primary and secondary coils is grounded to the coreThe other end of the primary connects to the insulated stationary breaker pointThe other end the secondary connects to the spark plugThe core and breaker point are grounded to the armature plateSECONDARY WINDING