2010 KAWASAKI Jet Ski STX-15F, Big-time four-stroke performance that won't break the bank When you break it down to performance per dollar, the STX.-15F jets right to the front of the pack. Its powerful Ninja.-derived 1,498 cubic centimeter engine delivers more smooth, four-stroke thrust than most riders will ever use, its race-bred hull design gives it the kind of championship-winning handling Kawasaki Jet Skis are famous.