Hunting Washington Forum

Other Activities => Fishing => Topic started by: huntergreg on May 28, 2011, 06:17:49 PM

Title: compression on a 15 hp mercury
Post by: huntergreg on May 28, 2011, 06:17:49 PM: Just wondering if anyone could tell me what the compression should be on a 1995 mercury 15hp. I have 96lbs in both cylinders. The motor runs great. I was told it should be 125lbs in each. :dunno:
Title: Re: compression on a 15 hp mercury
Post by: FC on May 28, 2011, 11:25:08 PM: Did you test with the throttle open? should be about 125-130 if it's a 2 stroke and probably 180-200 if it's a 4 stroke. Proper test is with engine warmed up and throttle open.
Title: Re: compression on a 15 hp mercury
Post by: huntergreg on May 29, 2011, 07:39:19 AM: I did the test when it was cold. I put the tester in the plug holes and just turned it over. Does warming it up make a difference?
Title: Re: compression on a 15 hp mercury
Post by: FC on May 29, 2011, 10:17:40 PM: Quote from: huntergreg on May 29, 2011, 07:39:19 AM
I did the test when it was cold. I put the tester in the plug holes and just turned it over. Does warming it up make a difference?

Yes, the rings expand and seal up a bit better, opening the throttle gives more consistent results and is the standard way to check compression.