help!

I have a merc sport jet 240 in my 2000 seadoo speedster, the boat is new to me so i am not sure what to do, it starts fine out of water but not in water. i noticed that both exhaust ports are fully submerged, i don't know if that is normal for this boat. Yesterday i pulled all the plugs out and...

at full speed bogs in and out of full throttle new fuel lines and cleaned filter above tank no difference had carbs rebuilt last year,

My '97 XP ran fine a week ago, but now when I gun it of idle speed it revs high and doesn't go very fast, then it catches up and starts moving. How fast is it made to go on a flat lake? Because it only hits 45mph. Thanks