I had the same problem with my boat it was bogging at WOT . I changed the plugs and added some fuel cleaner but the problem still existed. The next step was to dig into the carbs where the problem ultimately lied. Purchased some carb rebuild kits along with new fuel pump and in line filter. The old carbs jets were gelled over with carbon and soot. The filters were showing the same signs. I purged the fuel tank and installed rebuild kits per technical specs along with fuel pump. The boat now is running great knock on wood. The top speed has increased by a few knots as well. Hopefully this will help.