carb
hi i never tuned a carb on a boat but i will try to help. at 5 inch vac the power valves should be 2.5 ,3 max i would try that first . how far out are your idle mixture screw . how far open are your throttle plates with the carb off under the carb you should only see a small portion of the transfer slot below the plate you might hafe to drill your air bleeds more good luck let me know how it goes