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1975 Johnson 25hp. Running rough, won't idle low and won't reach full power under loa

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  • 1975 Johnson 25hp. Running rough, won't idle low and won't reach full power under loa

    I have a 75 25hp Johnson motor. It runs rough and won't idle low. It has no power under load. I've replaced all the coils, replaced condensers and points, new spark plugs, and fully cleaned out the carby. I'm at a lose as to y it is still running the same as it was before all the new parts. There plenty of compression too. Points are set too .020 and plugs are set to .030. Any help would be greatly appreciated. I have read through most of the forums already written about this. And I have done every thing it has told me. Still problems.


  • #2
    Re: 1975 Johnson 25hp. Running rough, won't idle low and won't reach full power under

    How is the spark and fuel delivery (pump output)
    Welcome to iboats.
    sigpicMarada 2100 Executive Series, 5 Litre V8 with Mercruiser Alpha 1 outdrive. 2007 K-Z Spree 260 RBH, all = a whole lot of family fun !!!!

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    • #3
      Re: 1975 Johnson 25hp. Running rough, won't idle low and won't reach full power under

      The spark is good. Nice sharp blue spark. And the fuel pump is pumping plenty of fuel. Bulb holds its pressure as well.
      Thanks for the welcome

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      • #4
        Re: 1975 Johnson 25hp. Running rough, won't idle low and won't reach full power under

        I reset the points gap and it idles fine now. But it's still not gaining its full power under load.

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        • #5
          Re: 1975 Johnson 25hp. Running rough, won't idle low and won't reach full power under

          How did you check your spark ?? Do a cyl drop test on it to make sure it's running on both cyls. How's the compression on it ??

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          • #6
            Re: 1975 Johnson 25hp. Running rough, won't idle low and won't reach full power under

            what do the plugs look like after a run at wot?
            many men fish for years without ever knowing its not about catching one.

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            • #7
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              Re: 1975 Johnson 25hp. Running rough, won't idle low and won't reach full power under

              I haven't looked at the plugs after wot, but the plugs are brand new.

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