Spark

Engine will not start

 Four stroke engine troubleshoot

For CDI systems that require no external source current to operate ignition (stand alone ignition)  .

Four cycle engine spark

Spark is produced at the spark plug through the following process

Magneto Flywheel

A magnet in the flywheel spins around the magneto also called the stator producing an electromagnetic field in the in the magneto.
This process can also work in reverse ( magneto spins in the flywheel)
Alternating current produced by the magneto travels to the CDI or capacitor.

The charge is stored in the CDI (Capacitor Discharge Ignition) and released when the trigger charge is received or at a predetermined time ( retarded or advanced spark).
 This discharge flows to a secondary coil that magnifies the voltage and emits a high voltage burst of current that flows to the spark plug and arks when it jumps across the spark plug gap.
This is the spark you see when testing for spark.

Check Spark  Plug
Fouled spark plugs may not fire
Clean or replace plug.
If plug is wet clear cylinder by turning engine over.

Check coil wire and boot connection.
Replace damaged wire or boot.
Press boot firmly onto spark plug.

Test Magneto

Test magneto resistance
Set meter to Ohms
If using an analog meter be sure to reverse leads when reading 0 and test again.
Place probes at beginning and end of fire coil
If reading is 0 coil is bad.
See example

Magneto test by output
Disconnect magneto
Remove spark plug (this will allow engine to spin faster)
Set volt meter to ACV
Place positive meter terminal on spark output wire (usually red w/ black stripe wire) in connector.
Ground negative meter terminal to engine.
Turn engine over
Using kick start 100V is satisfactory
Using electric starter 175V is acceptable.


Test CDI
 If possible install the CDI and test on a working system, if the engine starts the CDI is satisfactory. Or plug in a working CDI .
Resistance and continuity test can be done on some units
See examples
150-200cc CDI  Continuity

The following method is not recommended)
How 110 CDI Works
Disconnect CDI fire wire between CDI and coil
Set voltmeter to VDC
Using continuity setting can fry the meter
Connect a meter terminal to the disconnected fire wire of the CDI and the other to the coil wire.
Turn key switch on and spin engine.
Look for pulse reading with digital meter or needle bounce with analog meter.
If reading is 0 there is no circuit
If reading is bypass coil and connect to good ground
If  reading is 0 CDI may be bad.

Check Coil
Primary test
Disconnect coil
Set meter to OHMS or continuity
Read coil at primary
Coils with two primary leads test at the leads
Coils with single lead test at lead and ground to metal on coil or good ground
you should read a circuit


Secondary test
Set meter to OHMS
Test between primary lead and plug wire. Reading should be 6-9

 Spark plugs, coils and CDI modules are motorcycle engine components that can be used as diagnostic tools.
If possible keep one of each on hand.