1996 Johnson 90 hp compression

[rnhent12]

My compression runs 140 to 150 on all cylinders is that to high ?

 

[Chris1956]

The service manual cites a max of 20% difference between high and low compression readings. So it sounds like your readings are in spec.

BTW - compression testers are not all that accurate. They should, however, be reliable and read the same number for the same compression PSI. So it is possible for your cylinders to have a lower compression PSI, due to the inaccuracy of the gauge.

 

[metriccrescentwrench]

Most compression testers give fairly similar results, but of course it's possible to get ahold of one that reads high (or low).

Has this engine ever had modifications done to it (milling the heads for instance)? From my understanding of performance mods on outboards those kind of compression numbers are getting up to where you should be running high octane gas. Might be worth it to beg, buy, or borrow another quality compression tester and see if it gives similar readings.