25HP Merc Compression Leak? Any ideas?
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Posted by Mark (22.214.171.124) on October 03, 2004 at 11:51:52:
I have a 1988 or 1989, 25 HP tiller handle Mercury outboard that runs great. About every year, I replace the spark plugs and while I'm in there, I do a compression check. I've always had about 120 psi in both cylinders. Recently, I did a spark plug change and a compression check and discovered that something is leaking in the #1 cylinder. It builds 120 psi, but then my compression gauge indicates that the pressure slowly leaks out. The leak seems to be a bit slower if the throttle is open more, but it still leaks out. The #2 cylinder does not do this. It's a solid 120 psi.
The only thing that's different is that I had the carb professionally rebuilt since the last compression check (it had a leaky diaphram). The carb rebuild had no impact on the way the motor runs, but it now leaks some liquid fuel/oil mixture out the exhaust after each running. I don't know if any of this is related, but I thought it worth mentioning.
I'm trying to figure out whether I have a big problem (powerhead related), or a little problem. Do I need to park the boat until I get this fixed? Any help would be greatly appreciated.
Mark - Fayetteville, NC
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