Diagnosis help
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Thread: Diagnosis help

  1. #1
    Member Alewiska's Avatar
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    Diagnosis help

    Diagnosis??

    To recap, I was having issues with the left cylinder not firing. I swapped coils (left to right) and the right cylinder would not fire. I bought a new set of coils and when I kicked the bike over the left side would only backfire and sputter. I realized I hadn’t changed the plugs and when I pulled them, both were fowled. I put in new spark plugs and the left cylinder didn’t seem to be running. It took a little bit, but it definitely wound up firing, I could tell because of the heat on the left exhaust. Although, the left side was considerably cooler than the right. Took it out for a spin and the bike was really struggling not to die. Had to keep the throttle cracked a bit. As I was driving, on two occasions, when I pulled in the clutch to shift the bike died completely and almost instantly. If I dropped into gear if fired right back up. I just don’t know where to start. Valves, timing, compression, carbs? Can post a video tomorrow of the idle if it helps. Right spark plug showing really heavy signs of being too rich. Left spark plug almost looks brand new.

  2. #2
    Sensei 66Sprint's Avatar
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  3. #3
    Senior Member TOOLS1's Avatar
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    Sounds like an ignition problem. Also sounds like it is not running on one cylinder. Check to make sure that the coils are hooked up correctly.
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  5. #4
    Member Scramblr's Avatar
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    What year and model bike are you working? I would start by checking the ignition timing using a timing light against the rotor LF mark on the clutch side plug, and the F mark on the throttle side plug. From the symptoms you describe ignition might be the primary issue here.
    1975 CL360 K1 Scrambler

  6. #5
    Senior Member Polish's Avatar
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    Did you also check the idle? Could be why it dies when pull clutch, but the ignition/timing is probably the main reason it is not running correctly in both cylinders.
    JL
    1979 CB 400 T (Cafe Racer)

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