7.4
Section 7
Electrical System and Components
Figure 7-3. Capacitive Discharge (Fixed Timing) Ignition System.
Electronic CD Ignition System
Figure 7-4. Capacitive Discharge Ignition Module Schematic.
Kill Switch or
‘‘Off’’ Position of
Key Switch
Ignition
Modules
Spark Plug
Magnet
Flywheel
(0.28/0.33 mm)
0.011/0.013 in. Air Gap
L1
D1
C1
T1
P
S
Spark Plug
L2
SCS
Operation:
As the flywheel rotates, the magnet
grouping passes the input coil (L1). The
corresponding magnetic field induces energy into the
input coil (L1). The resultant pulse is rectified by D1
and charges capacitor C1. As the magnet assembly
completes its pass, it activates the triggering device
(L2), which causes the semiconductor switch (SCS) to
turn on. With the device switch
ON
, the charging
capacitor (C1) is directly connected across the
primary (P) of the output transformer (T1). As the
capacitor discharges, the current initiates a fast rising
flux field in the transformer core. A high voltage pulse
is generated from this action into the secondary
winding of the transformer. This pulse is delivered to
the spark plug gap. Ionization of the gap occurs,
resulting in an arc at the plug electrodes. This spark
ignites the fuel-air mixture in the combustion
chamber.
Troubleshooting CD Ignition Systems
The CD ignition systems are designed to be trouble
free for the life of the engine. Other than periodically
checking/replacing the spark plugs, no maintenance
or timing adjustments are necessary or possible.
Mechanical systems do occasionally fail or break
down however, so the following troubleshooting
information is provided to help you get to the root of
a reported problem.
CAUTION: High-Energy Electric Spark!
The CD ignition systems produce a high-energy electric spark,
but the spark must be discharged, or damage to the system can
result. Do not crank or run an engine with a spark plug lead
disconnected. Always provide a path for the spark to discharge
to ground.
Operation of CD Ignition System
Capacitive Discharge with Fixed Timing
This system (Figure 7-3) consists of the following
components:
• A magnet assembly which is permanently
affixed to the flywheel.
• Two electronic capacitive-discharge ignition
modules (Figure 7-3) which mount on the engine
crankcase .
• A kill switch (or key switch) which grounds the
modules to stop the engine.
• Two spark plugs.
The timing of the spark is controlled by the location of
the flywheel magnet group as referenced to engine top
dead center.
