Reply To: 1954 Johnson CD-10 5.5 HP – Magneto Armature Plate Grunge

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July 19, 2025 at 2:20 pm #298313
David Stanton
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    If the coils look good and the resistance test is good, they are probably good, but a resistance test doesn’t tell you if insulation is breaking down inside where you can’t see it, shunting the spark voltage to the core before it can build up high enough to jump the spark plug gap.  To test for this, you need an instrument that actually applies a pulse to the primary and shows you a spark jumping a gap, or a small neon bulb indicating spark generated.

    Dave