Polaris 2000 120 XCR, Service Manual

Page: 91 / 99

7.2
ELECTRICAL
IGNITION SYSTEM
OVERVIEW
The engine uses the U.T.C.I. (Universal type Transistor
Controlled Ignition) pointless ignition system.
BASIC THEORY
To ensure the easy starting of the engine, the step advancing
ignition timing system is incorporated in the ignition coil. This
system enables the engine to have basically two different
ignition timings according to the engine speed. Following are
the explanations of how this system works.
At lower engine speed, rotation of the flywheel induces current
I1, as this current flows through the base terminal of the power
transistor, it is activated and the current L2 is starts flowing. As
the engine reaches ignition timing, the ignition timing control
circuit for the lower engine speed is activated and lets the current
L3 flow through the base terminal of the power transistor. This
generates the collector current I4, which will bypass the current
I1 and abruptly shut off the current I2 because the power
transistor is turned off. This sudden current change generates a
high voltage on the secondary side of the ignition coil and which
sparks the spark plug.
At higher engine speed rotation of the flywheel generates the
current I1. As this current flows through the base terminal of the
power transistor, it is activated and the current I2 starts to flow.
As the engine reaches ignition timing, the ignition timing
control circuit for higher engine speed is activated and provides
the base current I5 to the power transistor. This current induces
the collector current I6 and will bypass the current I1 to shut
down the current I2 abruptly because the power transistor is
turned off. This sudden current change generates high voltage
on the secondary side of the ignition coil, which will spark the
spark plug. This ignition timing control circuit for higher engine
speed is activated sooner than the control circuit for lower speed
and is not activated when engine speed is in a lower range.