KG7 Lower Cylinder not firing

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  • December 30, 2025 at 5:44 pm #302813
    mark24
    Participant

      US Member

      Hello, I am working to improve operation of my KG7H that I run on a hydroplane. This summer, the lower cylinder was not firing well/at all as I was getting up to 30mph but not more! Could not get higher RPMs after tuning in the high speed jet. So, first I checked spark and it seemed like the lower plug spark was weak. It has been 20 years since I replaced the ignition wires and coils, so I thought I would do some work. Points open and close fine, Coils seem good (measured with ohmmeter). Condensers… might as well replace. Where can I get new condensers? What else would cause lower cylinder to not fire?  Bad compression resulting from lower seal leak?  I have not replaced the upper or lower seals …. since owning the motor for 40 years and running it a few times every few years. As I type that, maybe replacing seals would be a good idea. What do you think of this rant so far?  I do have the service manual, I guess I should read it.

      December 30, 2025 at 6:14 pm #302820
      mark24
      Participant

        US Member

        Using a video scope I see some rust at the top of the piston travel in the cylinder. Is that concerning?

        December 30, 2025 at 6:25 pm #302828
        Sam M.
        Participant

          Canada Member
          mark24 wrote:

          I have not replaced the upper or lower seals …. since owning the motor for 40 years and running it a few times every few years. As I type that, maybe replacing seals would be a good idea. What do you think of this rant so far?  I do have the service manual, I guess I should read it.

          I like the way you’re thinking! 😁

          I see some surface rust, so starting with something simple, are the points clean?  Also, I don’t think you’ll want to let the rust stay on the cam either, as the part of the points that touch the cam would probably prefer a smooth surface.  That way, the rust won’t act like sandpaper.

          1 user thanked author for this post.
          mark24
          December 30, 2025 at 6:28 pm #302829
          Sam M.
          Participant

            Canada Member
            mark24 wrote:

            Using a video scope I see some rust at the top of the piston travel in the cylinder. Is that concerning?

            If it were my motor, I would remove that rust, especially if a piston can touch it.

            1 user thanked author for this post.
            mark24
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