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70 HP Johnson compression test

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  • 70 HP Johnson compression test

    Just did a compression test on a 70 HP Johnson I picked up with a 16'
    what is a good number? i got 85 psi on top and mid & bottom was 70psi
    the motor is a '89 are these average for the year or should I be looking at new rings?

  • #2
    Re: 70 HP Johnson compression test

    I have a mid 80's 70 hp evinrude here. Compression is about 125 psi on each. As far as I have ever known (some may disagree, but I have always followed) once you get below 100 psi your getting border line on whether or not the motor is gonna run much longer.


    • #3
      Re: 70 HP Johnson compression test

      Are you doing it with a pull rope or starter? It's low if your doing by a starter, and they should all be within 10% of each other. There really is no magic number for compression. Certainly if your above 100 your good but it is more important that the numbers are within range of each other. Read the "Top secret" file at the top of the Johnson forum and do a decarb and then retest.
      The Crestliner Restoration


      1967 16' Crestliner and 60hp Johnny

      Klamath Trailorboat and 9.9 Johnny


      • #4
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        Re: 70 HP Johnson compression test

        Appreciate the advice, just checked the 'secret file' useful info. I didn't warm up at all, just cranked it over with guage in. I think a retry with warm engine is in order. Thanks again