Ignition Diagnosis for CB/CM 400/450 and CB450SC manual trans 1978-1986 - Page 2
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Thread: Ignition Diagnosis for CB/CM 400/450 and CB450SC manual trans 1978-1986

  1. #11
    Junior Member turfnsurf4ever's Avatar
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    HI Jim, IF the neutral safety switch is faulty, would the green neutral indicator light on the dash light up? Thank you.
    If I can't take it with me, then I am not interested...

  2. #12
    Super Moderator longdistancerider's Avatar
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    No, the light depends on ground thru the switch to work.
    Grounds can work but have too much resistance. Use a VOM set to volts. Check battery voltage at the battery posts then move the negative probe to the engine block and a frame ground connection. The voltage should read the same minus maybe .1V. If the reading are within that then the grounds are good.
    Jim O'Brien
    1979 CM400T "road bike" modified for travelling
    1978 CB400T1 restored
    1972 CL350 nuts and bolts restore in progress


    https://www.hondatwins.net/forums/22...d-attempt.html and https://www.hondatwins.net/forums/1-...r-attempt.html
    Road Trip https://www.hondatwins.net/forums/11...here-i-go.html or "where's Jim now?"
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  3. #13
    Junior Member SoapyCoyote's Avatar
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    I'm trying to test the spark plug wires with my ohm meter as per the sticky's instructions but I'm confused and would like some help please. I was able to unscrew the plug end caps just fine, they tested bad at like 50k 0hms so I ordered new ones. Thanks for that part number! Found them on amazon for about $6 and cange. But now I am unable to remove the actual spark plug wires from the source (is this called the coil? It's a black cylinder under the gas tank on the right side or "primary side" of the bike) to measure resistance of the wires themselves. How do you actually perform this test? I tried inserting one probe into each wire as the sticky says to do, and got nothing. Is this the right way to do this test, or should I continue to try to remove the spark plug wire and put one probe at each end of each wire treating the wires themselves as resistors? Also, if this is how you measure the resistance of each wire, how do I remove the coil end of the wire from the coil? Thank you in advance! So grateful for this information and sticky!

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  5. #14
    Junior Member SoapyCoyote's Avatar
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    Also, here is a picture. I'm attempting to unplug my spark plug wires from here
    Attached Thumbnails Attached Thumbnails Ignition Diagnosis for CB/CM 400/450 and CB450SC manual trans 1978-1986-img_0222_1492197330588.jpg  

  6. #15
    Junior Member SoapyCoyote's Avatar
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    Ok, I'm a total noob... I used google and learned that yes indeed modern day spark plug wires do have resistance. But I still don't know the best way to disconnect these ones from my coil. Any advice?

  7. #16
    Junior Member SoapyCoyote's Avatar
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    Are these spark plug wires the "non replaceable" type? I found this video on Youtube about how to replace non-replaceable spark plug wires. Any recommendations as to where to get the right kind of wire to use with the specified 7.2K ohms to 8.8K ohms of resistance?

    Here's the URL to the video:

    The guy uses a steel nail. I think I would want something more conductive like a brass nail or maybe copper.

  8. #17
    Super Moderator J-T's Avatar
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    The wires are permanently attached to the coil, not removable. If the coil/wires are bad you may want to consider the GM coil mod in another stickyl

    You had the right idea, one lead on the ohmmeter connected to each spark plug wire. Should read 7.2 to 8.8 K ohms. When you say you "got nothing" do you mean zero resistance or infinite resistance? Do you have an auto ranging multimeter?
    JT
    81 CM400T

  9. #18
    Junior Member SoapyCoyote's Avatar
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    Thanks for replying! Ok that makes sense. I'm sorry, I should have said I read infinite resistance. I tried poking the probes higher up, closer to the coil, and I still had infinite resistance on my ohm meter. It is auto ranging.

  10. #19
    Super Moderator J-T's Avatar
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    Cut the wires off until you can see fresh metal strands and re-check the resistance. If it still reads infinite you have an open circuit and a bad coil.
    JT
    81 CM400T

  11. #20
    Junior Member SoapyCoyote's Avatar
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    Yeah it reads infinite resistance across the two spark plug wires no matter how short I cut the wires. So GM coil mod? I think I found the thread on that. Thanks!

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