What type of gasoline should I use and how full should I fill the tank?

Use fresh, clean, regular unleaded gasoline with a minimum of 87 octane. Fill the fuel tank to the bottom of the tank filler neck and do not overfill. The fuel tank capacity is 4 gallons, and you should purchase fuel in quantities that can be used within 30 days to assure fuel freshness.

From the official Craftsman 917.275700 Lawn Mower manual, page 13

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