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Charging coil resistance?. 1980 Yamaha 40 BM

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  • #16
    I know I should have measured voltage to CDI, and used an inline spark monitor, but I am a very lazy electronics engineer :-). As to the two different symptoms, I supposed they both failed due to insulation breakdown and age, and the breakdown point was different for each coil?. One failing at low speed, the other high. Attached some pictures. The coil on the jig is NOT about to be wound, just showing how the jig works.
    Attached Files

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    • #17
      looks like you have plenty of wire on the spool.
      where did you come up with it

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      • #18
        Well there is good news, bad news and good news.
        The good news is that the rewound coil works perfectly.
        The bad news is that it wasn't the problem.
        The good news is I found and fixed the real problem.
        As can be seen on the foto, the one sparkplug lead from the coil showed a slight bulge. It seems vibration/heat might have caused the interior core to fail.
        The spark was strong enough to run 3/4 throttle but no more. But if it could then spark over the break, it was then maintained, so by getting the boat onto the plane, the motor could rev higher, causing the spark across the faulty section to be maintained?
        The arrow below shows the failed sparkplug lead.
        Attached Files

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        • #19
          reading the voltage inputs to CDI at failure would have indicated that the charge coil was not the problem and monitoring the output of CDI would have indicated the CDI was not the problem also.

          now finding the plug wire bad should have been found with a resistance check I believe.

          But glad to hear you got it going good again.
          and I am not sure many of us would have rewound our own coil.
          I am sure we all learned something from this

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