Craftsman 143.991200 Specifications download pdf (Page 56)

CHAPTER 8 IGNITION

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 it is released by an electrical switch (SCR). As

the magnet continues to rotate, it passes past 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 (diag.

1).

COMPONENTS

The solid state module is a complete unit that

includes the laminations and spark plug wire.

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 (diag.2).

NOTE: Always consult parts manual for correct plug

and reach.

GENERAL INFORMATION

Overhead valve four cycle Tecumseh engines use solid state capacitor discharge modules to provide high

voltage to fire the spark plug. This is an all electronic ignition system with all the components located outside

the flywheel. The modules look similar but are not interchangeable. If necessary, the correct replacement

module should be found using the Master Technician's Parts Manual.

The solid state ignition system consists of flywheel magnets and a flywheel key, charge coil, capacitor, a silicon

controlled rectifier, pulse transformer, trigger coil, high tension lead, and a spark plug. Everything except the

flywheel magnets, key and the spark plug are located in a encapsulated ignition module. This solid state (CDI)

module is protected by epoxy filler from exposure to dirt and moisture. This system requires no maintenance

other than checks of the high tension lead and spark plug.

STANDARD

PLUG

OHV

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Craftsman 143.991200 Specifications Page 56