454 crusader lagging when 4 barrel opens

Looking for a little advise on troubleshooting an issue i have experienced this season. I have a 1987 Silverton 37C with Crusader 350s (454ci). My starbourd engine (counter rotation) has been bogging down at around 3100rpm when the 4 barrel carb opens up. Its as though when under that load, the engine just will not produce anymore power, the rpms drop down to around 2700 then jump back up over 3100, all the while that the port engine is humming by at 3700rpm. I do not run the boat hard as she is an old gal, unless conditions dictate the need for additional power or speed. I would love to figure out what this issue is, as i fear blowing a piston. Ive run the fuel tanks dry, added fresh gas, changed filters. The engines are professionally maintained at a marina. Has anyone dealt with similar sounding issues? She has 1300 hours on her.

Ayuh,..... Sounds like the carb is goin' lean,.....

Might need to rebuild it,.....