I have a 1996 seadoo xp that runs good out of water but not in water to I did a compression test and found the back sparkplug is at 119 while the from sparkplug is at 105.
You will need to have the cylinders bored 1 size over, new pistons, rings and check the clearance on the rave valves when you do, they are good as they are for the first size over stock but will need to be machined if it’s the 2nd size over stock.