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81 XJ650 - Misfiring with Dyna Coils

Discussion in 'XJ Technical Chat' started by Tristan Kernick, Jun 29, 2025.

  1. Tristan Kernick

    Tristan Kernick Active Member

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    A few weeks ago, I posted about a misfire problem that stubbornly refused to go away until I undid my Dyna coil mod. Putting the OEM coils back on the bike fixed the issue, but now I have a new question. What could be going wrong with my Dyna coils?

    Here’s what I’ve checked so far:
    • Unscrewed and re-applied the plug caps
    • Removed the plug wires and cleaned the contact surfaces inside the coils. There was some corrosion inside one, so I thought this might be the problem, but the bike still misfires after cleaning it with fine grit sandpaper.
    • Checked the primary coil resistance. 20 kOhm on one coil, 19.5 kOhm in the other. Seems pretty good to me.
    So, what else can go wrong with these? I feel like the problem must be confined to the coils and wires, since the bike runs fine with the OEM coils. But who knows, maybe there’s something else going on.
     

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