I'm scratching my head. Even compression across all cylinders is best. What motor? It should run with 100 lbs of compression. Is it possible that one of the cylinder heads was replaced at some point or maybe surfaced? Either could mean different cc combustion chambers. If that be the case an easy fix would be to have the lower side head cut to make them more even or just find a matching pair. Being 20lbs off from port to starboard seems a little much. All my Mercs and Johnnyrudes are pretty even. +/- 5 lbs or less If memory serves the 90 Johnson only had 100 lbs after break-in with new rings and pistons. That was over a decade ago.. Sharper minds will chime in soon.
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1996 -19' NV Flats 115 Mercury 4-stroke
1983 -20' Wellcraft Center Console 250 XS
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