70 HP Johnson compression test

wetcoaster

Cadet
Joined
Aug 19, 2008
Messages
6
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?
 

CaptainHook

Petty Officer 1st Class
Joined
Mar 18, 2010
Messages
310
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.
 

Lion hunter

Lieutenant Commander
Joined
Apr 9, 2005
Messages
1,529
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.
 

wetcoaster

Cadet
Joined
Aug 19, 2008
Messages
6
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
 
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