175 Johnson low compression HELP

fsujack21

Seaman Apprentice
Joined
Jul 3, 2010
Messages
37
Hi everyone, this is my first post. thanks in advance for any help you can offer. I have an 89' johnson 175hp that during a trip late last season I picked up a bunch of seaweed in my canal that I believe covered the water intake. The engine was sluggish trying to get the boat on plane, then went into slow mode and probably overheated the motor, it smelled like burnt plastic, yet no alarm sounded. I didn't even try and start it, I just got towed back in. The next day I tried to start it, it turned over after almost an hour of messing with it and then cut out shortly after. I brought it home and left it until this season. (I know I'm an idiot for not winterizing it anyway, but I thought I blew it up and it wasn't worth my time)

This season I tried to check the compression but the flywheel was completely locked up. Lots of penetrating oil in the cylinders and some elbow greese I got the flywheel to loosen up.

I checked the compression on starboard bank I got 40 top, 60 middle and 120 bottom. On port side 90, 90, 82 from top to bottom. I pulled the starboard head and found what I thought to be some mild scoring on the top starboard cylinder wall and the other two looked fine the gasket was caked with salt water residue, but I couldn't see any obvious blowout. I cleaned everything up and replaced the starboard head gasket applied factory recomended torque hoping that would fix the problem. Now Im getting 48 top, 55 middle and 88 bottom? #1 did I install the gasket wrong? How did I get a drop on the bottom cylinder? #2 Where do I look next? rings? and if so how do I get to them? I have a sealoc manual but I seems to just tell you how to strip down the whole powerhead not fix individual problems. Thanks for any advice you can give.
 

wilde1j

Vice Admiral
Joined
Apr 15, 2002
Messages
5,964
Re: 175 Johnson low compression HELP

Well, maybe the scoring isn't so mild in the low hole. It's always possible ringws are stuck, and you might give decarbing a try if you can get it to run. Then recheck compression to see if any improvement. Sounds like a likely rebuild candidate.
 

fsujack21

Seaman Apprentice
Joined
Jul 3, 2010
Messages
37
Re: 175 Johnson low compression HELP

Sorry if i sound like a moron, but how do I de-carb it? I imagine some kind of spray they sell at west marine? To get the rings to be unstuck do I just douse it with more penetrating oil? does the motor have to run or can I get the oil/decarb stuff in there just by turning the flywheel by hand? Thanks again.
 
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