Your jet ski will not start but does turn over?

Check to make sure you have gas getting to the carburetor and spark on the spark plugs. Make sure the fuel selector is on and there's sufficient fuel in the tank to reach the pick up.

If you have gas and spark and the engine still won't start, you have to start looking for a problem. Start with measuring the compression in each cylinder.

There are a lot of specifics depending on what kind of jet ski you actually have. For example, if it's fuel injected, there's one set of procedures. If it's a 4 cycle, the steps are different from a 2 cycle. Usually, the owner's manual or shop manual will have troubleshooting steps.