20 HP Merc Loss of Power

[bmt1lawyer]

I have a 1989 Merc 2 stroke 20 hp. It starts first pull, idles fine, runs fine, but not sufficient power under a load (about the same power as my 9.5HP). It has good compression (100 psi) in both cylinders, good spark in both (bright blue), new plugs in both, runs on both (can pull either plug wire and still runs). The bottom plug is clean and dry, top cylinder plug is wet and oily, but obviously is firing enough to keep it running.

It has new clean fuel with 50:1. Throttle linkage working properly. But obviously there's something going on with the top cylinder. Could it be the carb? If yes, why just the top cylinder? Or maybe the reeds? Any suggestions would be helpful. Thanks.