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Change the oil at least once a year, more if you use it regularly. Spec on mine is every 100 hours of runtime. Adding a motorcycle hour meter is a cheap and easy way to keep track of actual engine runtime.
I put about 58 hours of runtime on mine last year, did an oil change because I hit the 1-year mark. As engine oil is used, it gets acidic and if an engine is used infrequently, that acidic oil degrades seals and mechanisms. If you know an engine is going to be sitting for a long time (dirt bike or lawn mower over the winter, etc) do an oil change in it so it's sitting with fresh oil.
Take care of your equipment and you can depend on it when you need it.
That's all I have for now, discussion and questions welcome.