6-1
CHAPTER 6. IGNITION
GENERAL INFORMATION
The ignition system consists of flywheel magnets,
flywheel key, charge coil, capacitor, resistor, a silicon
controlled rectifier, pulse transformer, trigger coil, high
tension lead, and a spark plug. Everything except the
flywheel magnets, flywheel key and spark plugs are
located in an encapsulated solid state Capacitor
Discharge Ignition module (CDI), outside of the flywheel.
This system requires no maintenance other than periodic
inspection of the spark plugs and high-tension leads.
OPERATION
SOLID STATE IGNITION SYSTEM (CDI)
As the magnets in the flywheel rotate past the charge
coil, electrical energy is produced in the module. The
energy is stored in the capacitor (approx. 200 volts) until
an electrical switch (SCR) releases it. As the magnet
continues to rotate, it passes a trigger coil where a low
voltage signal is produced. This low voltage signal closes
the SCR switch, allowing the energy stored in the
capacitor to flow to a transformer where the voltage is
increased from 200 volts to 25,000 volts. This voltage
follows along the high-tension lead to the spark plug
where it arcs across the electrodes and ignites the air-
fuel mixture. (Illust. 6-1)
COMPONENTS
The solid state module (CDI) is a complete unit that
includes the laminations, SCR, capacitor, resistor, pulse
transformer, charge coil, trigger coil, and spark plug high
tension lead.
The spark plug is made up of two electrodes. The
outside electrode is grounded and secured to the
threaded sleeve. The center electrode is insulated with
porcelain. The two are separated by an air gap, which
creates a resistance. A large voltage from the module
arcs the air gap, which causes a spark and ignites the
air-fuel mixture in the cylinder. (Illust. 6-2)
NOTE: Always consult parts breakdown for the correct
spark plug and reach.
6-1
6-2
The flywheel holds the flywheel magnets in a constant
position. It also provides rotational mass to smooth out
the effects of the engines power stroke.
The flywheel magnets: provides the magnetic flux (or
field) which is necessary to induce voltage and trigger
the module to provide spark.
The flywheel fins create air flow to cool the engine.
The flywheel key locates the flywheel to the crankshaft
in the proper position for ignition timing. Note: A sheared
or partially sheared flywheel key can cause kickback or
a No start condition.
NOTE: Always replace flywheel keys by model and
specification number. Keys that look similar may have
different timing dimensions or shear strengths.
STANDARD
PLUG
OHV
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