Compression differences top and bottom cylinder 1988 40 hp

lmuss53

Lieutenant Junior Grade
Joined
Sep 9, 2008
Messages
1,227
Top cylinder is 125, bottom is 140, is this something to be concerned about? This is just outside the 10 PSI or 10% commonly considered to be acceptable. I've checked it 3 times, ran it for about an hour or so in the tank, still the same. The motor has been used but not a lot recently. Should I do a decarb? Leave it alone? It is running good, starts right up idles good. I have not had it on the water yet.

Is there a preferred decarb method? I have been using a full can of Seafoam in 2 gallons of mixed fuel and running the whole 2+ gallons through the engines, it seems to clean the pistons when you look with a bore camera.
 

boobie

Supreme Mariner
Joined
Nov 5, 2009
Messages
20,826
Get a can of Engine Tuner from any BRP Evinrude dealer. Follow the directions on the can and see what happens.
 
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