Needed to brush cut my 1 acre prairie today. Mower is alway kept on my 601 which is always sheaded. It has be getting harder to start lately but once started ran real well. Today it was very slow to catch to the point where I got off the tractor to check the spark. Spark looked good (and felt strong too) and about the time I was feeling it it decided to fire. Warmed it up and backed out of the shed. Lots of condensation smoke coming out of the vertical exhaust. Never done that before. I decided to let it blow that off before beginning to mow. After 30 seconds or so there was a metallic ping out out popped an acorn. What the heck? Soon another followed and then it was just like a popcorn machine. Must have spit out about 50 or so acorns. After it finished upchucking the nuts, it ran smooth and strong. DANG RODENTS! There is a tin can sitting over the exhaust now.