I've read all of the replies about the cleaning of the Kawasaki engines and TOTALLY AGREE! I store my mowers in a 3 bay, open face shed, always covered. However that does NOT stop the mice from getting in under the shroud and building nests AND chewing wires. I did just pulled the shroud off and found a nest and and acorns. They also chewed the covering off one of the wires. Harbor Freight has liquid tape for around $20 which worked great.
During storage I do put moth balls in and around which acts as a deterrent.
But, like all the guys said, do this yearly which is EXCELLENT advice if not stored in a critter proof area or you DO run the risk of much more costly happenings later!