Honda HS928 Owner's Manual page 58

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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