“The last time I started it a bunch of acorns came out of the exhaust”, so, it has run in your hands! Now for the bad news, you probably shouldn’t have tried to start it. Mice can crawl all the way through the exhaust into the very depths of the engine itself. Mouse urine will cause things to rust and stick. Pushrods could have bent. Read the Stovebolt Tech Tip on resurrecting a long dead Engine for some do’s and don’ts.
When you get the engine all back together help will be here.