03 4 stroke 25hp bogging down

[shiver1]

motor runs great for about twenty min then loses power remains running but has no power. boat has set up for awile had some water in carb but cranks up easily and idles fine. when i cut it off and let i sit for as little as 30 sec it will run fine for another twenty mins or so. what could be the problem

[mitch]

clean your carbs sounds like muck on the pluck also check your fuel tank vent

[shiver1]

whats the best way to clean the carb and should my vent be open or closed