Reply To: 1960 40 HP – Bottom cylinder misfire

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October 28, 2026 at 1:19 pm #330632
TJ Brandon
Participant

    US Member

    I will test the compression when I get it put back together.

    I am sure it is the bottom cylinder because I have spark testers. Top is nice and consistent and strong while the bottom cuts out. I swap testers and the problem stays with the bottom cylinder. When the bottom does decide to fire it is nice and bright as well.

    For the cut out switch, i disconnected from the switch itself. There is a nut on a stud the ignition wire connects to. I removed that.

    A lower crank case seal can lead to poor ignition? How does that happen and how can I check? Upper crank seal I have replaced before and is easy to diagnose because of the mess it leaves on the magneto place