1971 Evinrude 40HP outboards Service Manual, Page 29Get this manual
DESCRIPTION MAGNETO The ignition system consists of flywheel type magneto connected to the spark plugs through high tension leads The magneto is self-contained electrical generating unit consisting of an armature plate with two ignition coil and lamination assemblies, condensers, and breaker assembliesA permanent magnet cast into the flywheel completes the assembly
THEORY OF OPERATION
The magneto employs the interaction of the fast moving flywheel magnet and stationary coil to generate an electric current of voltage sufficient to arc across the spark plug air gapThis creates the spark that ignites the fuel in the cylinder Each ignition coil actually consists of two coilsOne, called the primary, consists of relatively few turns of heavy gage copper wireThe other, called the secondary, consists of many turns of fine gage wireThe coils are separated by insulation and mounted on the center leg of an "E" shaped laminated iron coreOne end of both the primary and secondary coils is grounded to the coreThe other end of the primary coil connects to the insulated stationary breaker pointThe other end of the secondary coil connects to the spark plugThe coil core and movable breaker point are grounded to the armature plateSECONDARY LEADS TO BREAKE POINTS AND GROUND