I've recently restored an 85VT500C which had been sitting 15 years. I expect you will have to clean the carbs especially the jets but probably can rebuild it with replacing. You will likely need a new rubber kit though (bowl gaskets and pilot screw o-ring). Be sure to clean all the tiny holes in the jets as Kenstone above says. To clean the rust from the tank I would use a product called evap-o-rust.