merc sportjet 90 won't start in the water

[nathan20328]

I have a 94 regal rush jetboat with a merc sportjet 90. It starts/runs fine on dry land (very short periods of time with no water hooked up). When in the water, it'll start and run rough if you take off immediately, but if you turn it off, it won't start back up in the water...only after a long period of time (a day or more) out of the water. Am I getting water in the fuel somehow...? What might be causing it...? I'd be thankful for any ideas on this.