Octane does not degrade or decrease over time. The fuel itself can degrade as it can collect moisture or can start evaporating some, and ethanol makes is lightly worse. With that said any typical gas is usually formulated to last at least a year (based on some sort of ASTM or the like parameters most likely) without any major issues. I regularly have small engines (mowers, etc...) that may sit 5-6 months unused and have never had an issue, and that is with typical 87 octane pump gas with ethanol. I have a 15 HP Briggs on a mower from the mid-90's that has always runs this type of gas since new and I can't even remember the last time the spark plug was changed (at least 7-8 years), then I have a 20 HP Kawasaki twin on another '98 model mower that I've owned for around 8 years. This spring was the first time I changed the plugs just for maintenance reasons and noticed no difference in performance.Premium is not really a waste in the small engines, as they are not used everyday like our cars. The octane rating begins to degrade fairly quickly in lower octane fuel and with not much time it can be way lower than the 87 the engines are designed for. The higher octane fuel takes longer to start degrading, so even if it sits you should still have the 87 octane the machine requires. Once I switched to ethanol free premium in all my equipment I have not had any more fuel/carburetor related issues.
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