Only 4500 -4800 RPMS- 90 HP Johnson on 20'SF

[Texascoastalfish]

Update. I should have checked compression from the get-go.
After not getting above 4900 RPMS with still a 17P prop and motor 1" above keel, I checked compression and I found bottom portside cylinder 70 PSI all the rest had 120. Pulled head and found no visual damage, bore seemed smooth , no gouging, I did find a very small piece of aluminum in the head dome. Decarbed Cylinder 2X with Seafoam, no change. Put some 30 wt oil in cylinder and compression jumped to 90. Bad Ring(s). In stead of pulling powerhead and rebuilding 1 or all cylinders I opted for a little more HP and got a totally rebuilt, bored over and fully warrantied 1995 112 SPL from a local marine motor shop (cash is king these days, bargains abound) Its now more like a 120 HP due to .020 boring and bubbleback exhaust Vs. Flatback exhaust. Had it rigged yesterday and I'm ready for the break in procedure. I will hopefully be in the 5500 RPM range by Sunday I stuck with the 17P prop for the higher HP. I now have 90 Johnson on Craigslist and if I cant sell it for 750 bucks I'll rebuild and put it on a skinny water skiff like an Explorer or something real shallow. Never can have TOO many boats. ( in the end maybe 1 less wife if this keeps up !)