If it were me I'd put a tablespoon of Marvel Mystery Oil top cylinder lube down each plug hole and let that sit for a day, then gently turn it over twice and let it sit another day before I tried anything with the motor.
Drain the tank and the carbs, pull the petcock and clean it. You might just be able to get away with running a tank of double strength Seafoam through to clean the fuel system, but, after 25 years I'd bet that you really need to pull the carbs and given them a thorough cleaning.
