Honda BF75, BF100, BF8A Outboard Motors Shop Manual, Page 113Get this manual
CONSTRUCTION AND FUNCTION
ELECTRICAL SYSTEM
Ignition System
A CDI (Capacitor Discharge Ignition) system is employed in motor with engine serial number 1200001 subsequentIt uses semi-conductor switching element called "SCR" for Silicon Controlled Rectifier, or more commonly"thyristor"OPERATING PRINCIPLE
1With the engine runningthe flywheel magneto (1) induces alternating current in the exciter coil (2) Positive half-cycle current flows in direction i1through diode D1in the CID unit to charge the capacitor (3) 2When the advancer rotor (4) in the cam pulley (5) turns to the ignition position alternating current is induced in the pulser coil (6) The current flows in direction i2 through diode D2 and triggers the thyristor (7) into conductive statecausing the capacitor (3) to discharge into the ignition coil (8) 3This momentary inrush of discharging current induces high voltage surge in the ignition coil secondary winding causing spark the plugs (9)