Pull the spark plug out, turn your bike upside down & drain all the water out of the motor, get it right side up again & pour some atf or diesel fuel in the plug hole,rinse, drain, repeat, until all the rust & smut is gone, with the bike on a stand, put the trans in high gear & rotate the rear wheel, back & forth. It may free up & spin, but I doubt that it will start or run for long if it does. Tear it apart & re-build it, or buy an other motor on ebay or a bike salvage Co.