Service Manual

ELECTRICAL SYSTEM 9-17
Ignition System
This engine ignition is controlled by a solid state ignition assembly and requires no periodic main-
tenance 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: Magnet
N: North Pole
S: South Pole
Ignition System Operation Theory
Permanent magnets are mounted around the edge area of a flywheel. As the flywheel (magnetic
pole) rotates clockwise and passes the ignition module on a laminated core group, voltage is produced
at the primary winding (L1), allowing a small bias current to flow from the control resister (R1) to the
transistor (Q1) base and thereby exciting the transistor base. Thus the transistor forms (turns ON)
the primary circuit. This circuit current flows from the plus (+) side of the primary winding to ground
through the transistor [Collector (C) to Emitter (E)].
When the base current is flowing, the trigger sensor (TS1) detects optimum time (peak current) to
shut off the transistor base current. With the transistor rapidly shutting off the current at the primary
coil, counter-electromotive force is generated and voltage in hundreds-volts is induced through the
primary winding (L1), thereby producing extremely high voltage at the secondary winding (L2). When
this secondary voltage steps up to k-volts, “ionization” meaning “ignition” occurs across the electrodes
at the spark plug (SP).
The trigger sensor located internally in the ignition system is set to give constant ignition timing
according to engine speed and temperature.
The diode (D1) located at the ignition shut-off circuit prevents misconnection of battery voltage,
protecting the internal components of the ignition system. When the stop switch (SW) is set at the
closed position, primary voltage is routed to ground, not allowing igniting operation.