Well there is half a million things it could be so lets start with the basic comporession test because we know it has some fuel and spark - look for something higher than 130 and both need to be very close to each other, then look at the water/fuel bowl under the glove box for steel gas can trash or goop that comes from the grey lines - this has been a well known trouble maker but by this time in jetski life they have prolly been replaced, then there are small fuel filter screens inside the carbs that are the last place for the goop to land before gooping up the inner workings of the carbs themselves. Use the pictures in the parts places to identify the parts for your individual model.