Service Manual

8-14 ELECTRICAL SYSTEM
Charging, Ignition System
This engine ignition is controlled by a solid state ignition assembly and requires no periodic maintenance except for the
spark plugs.
The system consists of the following:
Inductive Ignition Assemblies
Permanent Magnet Flywheel
Spark Plugs
Stop Switch
Co: Core (Lamination)
D1: Diode
L1: Primary Coil
L2: Secondary Coil
Q1: Transistor
B: Base
C: Collector
E: Emitter
R1: Control Resistor
TS1: Trigger Sensor
SP: Spark Plug
SW: Stop Switch
F: Flywheel
M: Magneto
N: North Pole
S: South Pole
Ignition Theory of Operation
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 (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 constant timing over speed and temperature
and prevents counterclockwise operation.
The diode (D1) in the ignition shut off circuit blocks inadvertent application of battery voltage, protecting the internal
components of the ignition. With the stop switch (SW) in the closed position primary voltage is routed to ground, preventing
ignition operation.