Ignition Theory of Operation -Kawasaki FH451VFH680V

Mounted to the periphery of a flywheel are a pair of magnetic poles (south leading in clockwise rotation), generated by a permanent magnet. By rotating the flywheel (magnetic poles) clockwise past the ignition module on a laminated core group, a voltage is generated in the primary winding (L1). This generates a small bias current to flow through the control resistor (R1) to the base of the transistor (Q1). This base drive causes the transistor to conduct (turns on) completing the primary circuit. Current flows from the high side of the primary winding through the transistor (collector to emitter) to ground. The trigger sensor (TS1) senses the optimum time (peak current) to remove the base drive from the transistor (Q1). This abrupt “turning off” of the transistor causes an interruption in current flow which allows its associated flux collapse, and several hundred volts is induced through the primary winding (L1) inducing a very large voltage in the secondary winding (L2). When the secondary voltage reaches several thousand volts, the spark plug (SP) gap is ionized and ignition occurs. The placement of the trigger sensor internal to the ignition insures the constant timing over speed and temperature and prevents counterclockwise operation. The diode (D1) in the ignition shut off circuit blocks the inadvertent application of the battery voltage, protecting the internal components of the ignition. With the stop switch (SW） in the closed position, the primary voltage is routed to ground, preventing the ignition operation.