Honda FC600 Owner's Manual page 45

The Distributor's Limited Warranty does not cover fuel system damage or
engine performance problems resulting from neglected storage preparation.
You can extend fuel storage life by adding a gasoline stabilizer that is
formulated for that purpose, or you can avoid fuel deterioration problems by
draining the fuel tank and carburetor.
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.
STORAGE
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