1995 Seadoo Xp 720 Problems?? HELP PLZ!?!?

[Beebe]

HI, I have a 1995 Seadoo Xp that I recently just bought used. The ski has a brand new engine. The exhaust manifold bolts kept comming loose. The threads on the head were stripped. So we had it professionally drilled and tapped to the next sized bolt. Now my problem. We fixed the exhaust and we cleaned the inside before taking it out again. I ran it for about 10 minutes then i noticed like a soft poppin sound under the seat. We adjusted the carbs and everything we could think of. It will start and run out of the water, but as soon as hits water it will shut off. Both plugs have spark and just put brand new ones in. Does anyone have a clue what could be wrong? Also, the gas guage was working when i first got it. When i filled up the tank, the light never came off. Anyone know what happend? Magnets? Thanks.