Good compression ?
Printed From: The Fishing Website
Category: General Forums
Forum Name: The Outboard Clinic
Forum Description: Anything related to outboard maintenance here....
URL: https://www.fishing.net.nz/forum/forum_posts.asp?TID=133006
Printed Date: 10 Jun 2026 at 4:58am
Topic: Good compression ?
Posted By: Judokapont
Subject: Good compression ?
Date Posted: 26 Feb 2020 at 5:54pm
G’day
I was wondering what you guys would consider decent compression for a 1998 Johnson 90hp ?
Cheers
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By the power of Greyskull
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Replies:
Posted By: Steps
Date Posted: 26 Feb 2020 at 6:17pm
1st make sure measure correct.
2005 manual
" 1/ run out board till full operating temp reached, shut down
2/disconnect crank shaft position sensor
3/move throttle linkage to WoT
4/ turn over on starter measure max pressure on each cylinder
Sry cant find pressure specs.. I would think around the 115lbs ???.. Thu what looking for is difference between cylinders. Anything over 10/12% indicates something wrong.
Also a engine that has a build up of carbon in the chamber has a higher compression, assuming that the rings etc in good condition .. hence why looking at the variation.
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Posted By: smudge
Date Posted: 26 Feb 2020 at 6:56pm
What were your results Judo?
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Best gurnard fisherman in my street
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Posted By: Judokapont
Date Posted: 26 Feb 2020 at 7:33pm
Thanks for the reply Steps and Smudge
I had my outboard serviced and on the report it says
1) 125
2) 120
3) 125
4) 120
Cheers :)
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Posted By: Steps
Date Posted: 27 Feb 2020 at 8:54am
I would be very happy with that.
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Posted By: Judokapont
Date Posted: 27 Feb 2020 at 12:56pm
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Excellent news , thanks Steps
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Posted By: Nickb1
Date Posted: 01 Mar 2020 at 8:09am
the biggest thing is that you don't want a big variation between them.
5 ether way is fine but if you had 1 cylinder showing 107 lets say, that could indicate an issue.
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