Honda HS724 Owner's Manual page 54

STORAGE
Adding a Fuel Stabilizer to Extend Fuel Storage Life
When adding a fuel stabilizer, fill the fuel tank with fresh gasoline. If
only partially filled, air in the tank will promote fuel deterioration during
storage. If you keep a container of gasoline for refueling, be sure that it
contains only fresh gasoline.
Add fuel stabilizer following the manufacturer's instructions.
After adding a fuel stabilizer, run the engine outdoors for 10 minutes to
be sure that treated gasoline has replaced the untreated gasoline in the
carburetor.
Stop the engine, and move the fuel valve lever to the OFF position.
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