Please note this thread has been inactive for 90 days. For the best results, please start a new thread.
Results 1 to 4 of 4
  1. #1
    Cadet
    Join Date
    Aug 2008
    Location
    Qualicum Beach BC
    Posts
    6

    Default 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. #2
    Petty Officer 1st Class
    Join Date
    Mar 2010
    Location
    South East Pa/ Chesapeake, MD
    Posts
    309

    Default 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. #3
    Lieutenant Commander Lion hunter's Avatar
    Join Date
    Apr 2005
    Location
    Idaho
    Posts
    1,528

    Default 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

    http://forums.iboats.com/showthread....49#post2218249

    1967 16' Crestliner and 60hp Johnny

    Klamath Trailorboat and 9.9 Johnny

  4. #4
    Cadet
    Join Date
    Aug 2008
    Location
    Qualicum Beach BC
    Posts
    6

    Default 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

Similar Threads

  1. compression test on 1999 Johnson 90 hp
    By big moe in forum Johnson & Evinrude Outboards
    Replies: 1
    Last Post: July 9th, 2010, 06:34 AM
  2. 1980 Johnson 140 hp compression test-how
    By Jim Robbins in forum Johnson & Evinrude Outboards
    Replies: 1
    Last Post: August 9th, 2007, 04:44 PM
  3. Compression Test ? 86 Johnson 150hp
    By Pst76 in forum Johnson & Evinrude Outboards
    Replies: 3
    Last Post: April 2nd, 2003, 11:33 AM
  4. Compression test for '83 Johnson 60 HP
    By Archer440 in forum Johnson & Evinrude Outboards
    Replies: 1
    Last Post: May 4th, 2001, 06:41 PM
  1. iboats Forum Directory - Over 100,000 forum posts organized by topic