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How are you doing the compression test? I always check the compression three times through with a full charged battery engine cold 1-4 1-4 1-4 and use the high number for each cylinder. Crank the starter until the compression guage stops moving. Seafoam will clean up the rings and valves. Bring the engine up to normal temp and the at around 2000 rpms pour half a can of seafoam down the carb at a rate to almost stall the motor and quickly shut it down. Throw a line in the water and wait at least 1/2 an hour then point the boat at the big part of the lake and run it WOT for 20 minutes to blow the cobwebs out. If you not able to reach proper WOT rpms it may be over propped causing the engine to carbon up. Check the compression again and see if the numbers even out.
IMO, we should never operate any Marine Engine at WOT RPM for any longer than what's necessary while checking for correct propeller pitch and/or ratio........ 10 to 15 seconds should be long enough.
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