Ignition Diagnosis for CB/CM 400/450 and CB450SC manual trans 1978-1986
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Thread: Ignition Diagnosis for CB/CM 400/450 and CB450SC manual trans 1978-1986

  1. #1
    Super Moderator longdistancerider's Avatar
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    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

    Stator Tests:
    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.

    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.

    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.

    The stator ohm readings listed can be off no more than 1 ohm, more than that will have a negative effect on the timing advance

    Run/Kill and Ignition switch Tests:
    Connect one probe to the Black w/White tracer pigtail wire coming out of the CDI unit. Connect the other probe to the negative battery terminal
    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 selectable. If you have to select the range be sure to do that matching the expected ohm range.
    Last edited by longdistancerider; 08-16-2016 at 04:00 PM.
    jbc2408 likes this.
    Jim O'Brien
    1979 CM400T "road bike" modified for travelling
    1978 CB400T1 restored
    1972 CL350 survivor restoration

    SALE IS ACTIVE TILL 200 SHIRTS SOLD T-shirt sales supporting 66Sprint's Land Speed Record Build http://www.hondatwins.net/forums/22-...d-attempt.html

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  2. #2
    Senior Member dtsmjr8dan's Avatar
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    This is what the group has needed for a while, Jim. It's been meted out in bits and pieces, but, having it all in one sticky is awesome.
    jbc2408 likes this.
    1979 CM400T (rider),
    1981 CM400T (in surgery receiving transplant)
    1982 CM450 (parts bike)
    1982 CB450 (parts bike)
    Past rides: Vincents, Triumph, BSA's, Suzuki's, Twingle, Corgy, others.
    Remember, today is the tomorrow we worried about yesterday.
    My chest fell, but, fortunately, my belt caught it.
    I don't know everything, nor, have I met the one who does.

    T-shirt sales supporting 66Sprint's LSR Build http://www.hondatwins.net/forums/22-...d-attempt.html

  3. #3
    Super Moderator longdistancerider's Avatar
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    I've been meaning to do this for awhile, finally got around to it.
    Jim O'Brien
    1979 CM400T "road bike" modified for travelling
    1978 CB400T1 restored
    1972 CL350 survivor restoration

    SALE IS ACTIVE TILL 200 SHIRTS SOLD T-shirt sales supporting 66Sprint's Land Speed Record Build http://www.hondatwins.net/forums/22-...d-attempt.html

    http://www.hondatwins.net/forums/22-...d-attempt.html and http://www.hondatwins.net/forums/1-p...r-attempt.html
    Road Trip http://www.hondatwins.net/forums/11-...here-i-go.html or "where's Jim now?"
    Member Map http://www.hondatwins.net/forums/dcMembermap.php

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