low compression in bottom hole

[richardreyn78818]

i have a 2005 Mercury 90 4-stroke 20" with compression readings of
145
135
145
95
can this be fixed? thanks rich.

 

[Dave1027]

Re: low compression in bottom hole

Squirt some motor oil into the cyl and test again. That will tell you if it cyl/rings or valves.

 

[Jlawsen]

Re: low compression in bottom hole

The old squirt oil in the hole and test may work but you're dealing with a fairly advance 4 stroke motor and the best bet is to order the shop manual and do the diagnostics tests. There are a half dozen things that can cause low compression in a 4 stroke and the old stand by oil test, when done correctly will give you a general idea but could also take you completely off track. I won't tell you that I don't do it because I do but I also follow through with all the other tests in the manual before I make a decision to repair or replace.