BRP Johnson 4HP, Service Manual, Page: 44 / 185

3-2
IGNITION AND ELECTRICAL
IGNITION SYSTEM
IGNITION SYSTEM
Outline
A digital CDI (condenser discharge ignition) system is used on all models. The CDI and coil unit incorpo-
rates an ignition coil and pulser core. If the magnetic reluctor bar on the flywheel passes through the
pulser core, the exciter coil in the unit generates the electrical energy as shown in the chart below.
The condenser stores the positive side electrical energy, while the CPU utilizes the negative side electri-
cal energy as basic signals in order to calculate the engine speed and to control the ignition timing.
The electrical energy stored in the condenser is released to the ignition coil primary windings, then a
high surge voltage occurs in the ignition coil secondary windings and spark is generated.
The CDI and coil unit incorporates an over-revolution limiter which limits maximum engine speed to
approximately 6000 r/min. If the over-revolution limiter activates, the motor will exhibit a rough running
condition.
SPECIFICATION
IGNITION SIGNAL CHART
UNIT INTERNAL STRUCTURE
Ignition type CDI
Advance Electronic microcomputer control
Ignition timing BTDC 3° – 28°
Exciter coil output
POS.
NEG.
BTDC 10°
Basic signal
Ignition signal
360° of crankshaft
1 Exciter coil
2 Power source circuit
3 Basic signal circuit
4 Hardware ignition signal
circuit
5 Ignition coil
Spark
plug
Condenser
Stop
switch
SCR
CPU