Not trying to be funny.
the site apparently will not let you embed links, so you will have to put this one together.
google this phrase > seadoo shop manual > it will be the first link, free download, get an appropriate manual.
start with a compression test.
1 st problem sounds like fuel, now is the time to go through it , new selectors, fuel filter assemblies, fuel line, rebuild carbs, not hard\ < maybe even pickup / baffle if the connections look bad.
really just a few Saturdays of tinkering, you will spend more time reading the instructions for the carb rebuild than it will take you to do it.
when you open up the old carbs, remove strainer and inspect, probably going to be full of junk.
need to check pop-off , easy to build a tool on that one, do you own an air compressor?, you will have to make a screw driver to get the low jets out, I usually just take a grinder and whittle one down.
but really , you could just pull the carbs and mail them to someone for rebuild, it is a little job, very easy, probably $200 in labor at my rate.
but always start diagnosis with a compression test, post back results, try to get it from a snap on gauge, if you do not have one pick one up NOW if you are going to stay in this hobby.
just ask if you have any more questions.
I would also buy some otiker pliers off ebay < double sided, and place an order to McMaster for clamps.