pair of GTS's or GS's? The GS was only a 717 from 97-00 and the GTS was around from 92-2000 and got the 717 in 1997. Only reason I'm saying this is because we need to know what exactly you have.
With that said-
What are the compression numbers for each cylinder?
Does the ski still have gray fuel lines?
Have you cleaned the carburetor at all? (There is a small filter inside the carb, as well as one under the handlebars, above the fuel tank)
These three things need to be addressed. As for the hose not connected to the exhaust, it is likely a cooling water hose and needs to be connected. If not, it is flooding the hull with water as you ride. If it is missing entirely then it still needs to be installed.