'99 Mercury 90HP 2 stroke, little help needed

[hfd410]

This engine is on a '99 Ranger. It has been ran regularly for quite some time. For the last several months it will only run out to 4200 rpm in gear but will rev to over 6000 out of gear. Was bogging a little bit out of the hole. It used to run wide open on the water at well over 5000 from what I remember. Also, every once in a while and very infrequently at WOT it will surge and run at 5200 or so for a few seconds.

I have done the following: new fuel lines including the oil injection hose prior to the pump, overhauled fuel pump, cleaned carburetors and replaced all gaskets and float valves, verified linkage is all in at WOT, verified spark and compression, replaced primer bulb. After carburetor overhaul it runs better and doesnt bog but it will not reach max RPM. I toyed with the idle mixture (all at 1.75 turns out) and the top carburetor seemed to affect the idle more than the others. Any help appreciated.

[boats.net]

Probably plugged jet or passage in one of the carbs restricting fuel to one cylinder or ignition problem on one cylinder. See if any spark plug show lean burn condition, might can tell which cylinder is not running.