Honda EU3000is Owner's Manual page 64

STORAGE
Adding a Gasoline Stabilizer to Extend Fuel Storage Life
When adding a gasoline 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.
1. Add gasoline stabilizer following the manufacturer's instructions.
2. After adding a gasoline stabilizer, run the engine outdoors for 10
minutes to be sure that treated gasoline has replaced the untreated
gasoline in the carburetor.
3. Stop the engine, and turn the fuel valve to the OFF position.
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