220 crusader won't go over 2300 rpm

by Captain Joe
(Stuart, FL 34994)

I have a pair of 220 hp Crusaders in a 32' Chris Craft express. Starboard engine fine, port engine won't go over 2300 rpm and then knocks like bad gas or timing. Already did: swapped carbs - no difference, changed all filters - no difference, all new gas - no difference, changed intake manifold gaskets, maybe a vacuum leak - no difference, checked advance weights - seem to be advancing - no difference, re-adjusted all valves - no difference, Checked timing with light - seems OK - no difference. Any ideas captains

Joe, dreamwavesinc@comcast.net