56
IGNITION AND ELECTRICAL
OPERATION
When the recoil starter is pulled, the flywheel is turned. An electromotive force generated in the primary
winding (n
1) of the ignition coil makes the transistor (TR1) conduct through the resistor (R1) and forms the
primary circuit (indicated by dashed lines).
As the flywheel turns further, the primary current increases, and the terminal voltage of the circuit con-
sisting of the resistor (R
1) and transistor (TR1) increases. This increases the working voltage at the con-
nection of the series circuit (R
2 and R3) connected in parallel to the primary circuit. As the flywheel turns
further, the terminal voltage of the resistor (R
3) in the resistor circuit (R2 and R3) rises to the level of work-
ing voltage of the transistor (TR
2) when the ignition timing approaches, and thus the transistor (TR2) is
turned on. As a result, the base current of (TR
1) flowing through the resistor (R1) is bypassed, and the
transistor (TR
1) is turned off from the conductive state.
The current flowing through the primary winding (n
1) is thus interrupted, and a rapid change occurs in the
magnetic flux across the ignition coil. The result is a high surge voltage in the secondary winding (n
2).
Transistor
Flywheel
magneto
Ignition
coil
Spark
plug
Emergency
stop switch
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