Ignition Diagnosis for CB/CM 400/450 and CB450SC manual trans 1978-1986
These tests are used to check the CDI system. There are no valid tests for the CDI unit so this is an elimination process. If all these tests are good then the CDI is at fault. Before replacing a CDI all these components have to test good.
Use a multi-meter and set it to measure electrical resistance in Ohms.
Coil Test:Primary Side.Measure the resistance between the Yellow and Green wires.
The Yellow and Green wires being measured will be coming out of the spark plug coil.
The resistance should be less than 1 Ohm. Spec is .35 to .55 ohms
Secondary Side: Measure the resistance of the spark plug wires with the plug end caps removed, they unscrew. Insert a probe into each wire. Spec is 7.2K ohms to 8.8K ohms
Plug End Caps: Measure the resistance of the plug end caps. Spec is 5K ohms. Replacement part number is NGK XD05F
The connectors used are found under the left side cover
Measure the resistance of the Pink and Green wires.
The Pink and Green wires to measure will be going into the bundle that goes along the frame and eventually to the stator. This is the advancer pickup sensor
The resistance should be about 135 Ohms. New Spec 129 Ohms
Measure the resistance between the White and Blue wires.
These wires to measure will be going along the frame and eventually to the stator also. This is the CDI power source
The resistance should be about 85 Ohms. New Spec 84.2 Ohms
Measure the resistance between the Brown and Light blue wires.
These wires to measure will be going along the frame and eventually to the stator also. This is the primary pickup coil, the aluminum piece outside the rotor
The resistance should be about 207 ohms. New Spec 203 Ohms
The stator ohm readings listed can exceed the old spec by no more than 1 ohm, more than that will have a negative effect on the timing advance.
The New Spec was obtained by measuring 2 NOS stators, fresh unused old stock early model with the bullet Blue and White wire connectors.
Run/Kill and Ignition switch Tests:
Connect one probe to the Black w/White tracer pigtail wire coming out of the main wiring harness that connects to the CDI unit. Connect the other probe to the negative battery terminal. The results should be:
Ignition switch on, Run/Kill switch in Run position: Infinite Ohms reading meaning an open circuit
Ignition switch on, Run/Kill switch in Off position: Zero ohms or close to that showing the circuit is closed/completed to ground
Ignition switch OFF, Run/Kill in any position: Zero ohms or close to that showing the circuit is closed/completed to ground
Alternator Tests: Select/connect to one Yellow wire with a probe. Connect the other probe to one of the remaining 2 Yellow wires, resistance should be below 1 ohm. Repeat twice using a different wire each time. If the readings are good then test each of the Yellow wires with one probe connected to ground. There should be an Infinite ohms reading meaning none of the charging coils is shorted to ground.
NOTE: Some VOM's are auto-ranging meaning they switch ohm scales as needed and some are range selectible. If you have to select the range be sure to do that matching the expected ohm range.