From your original post, it sounds like you just bought this ski. Was a compression test done? Did you receive any transfer of knowledge. Especially, in regards to the service history? If not, there are plenty of threads here advising what should be done on these old skis. Before doing anything, do a compression test to confirm what shape the motor may be in and what you have to work with. If that tests ok, Primary area of concern if you do not want to toast the engine, is the fuel delivery system and using the right oil. Before running it anymore, replace any old gray tempo fuel lines and rebuild the carbs ( sticky how-to is on this forum) . Replace fuel selector valve and water separator filter. Clean and inspect fuel vents. Do not mix oil brands. Find out what kind the PO was using and either keep using (if it is the right kind) or drain the system and replace with correct kind. Also, replace inline oil filter. Bleed the system.
That should get you started on preparing an older model ski for a lot more fun.
