Honda and WT40X Owner's Manual page 45

STORAGE
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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.
1. Add fuel stabilizer following the manufacturer's instructions.
2. 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.
Dry operation will damage the pump seal. Be sure the pump
chamber is filled with water before starting the engine.
3. Stop the engine, and move the fuel valve lever to the OFF position.
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