Honda Harmony II HRT216PDA Owner's Manual page 46

Fuel
Gasoline will oxidize and deteriorate in storage. Old gasoline will
cause hard starting, and it leaves gum deposits that clog the fuel
system. If the gasoline in your mower deteriorates during storage,
you may need to have the carburetor and other fuel system
components, serviced or replaced.
The length of time that gasoline can be left in your fuel tank and
carburetor without causing functional problems will vary with such
factors as gasoline blend, your storage temperatures, and
whether the fuel tank is partially or completely filled. The air in a
partially filled fuel tank promotes fuel deterioration. Very warm
storage temperatures accelerate fuel deterioration. Fuel
deterioration problems may occur within a few months, or even
less if the gasoline was not fresh when you filled the fuel tank.
The Distributor's Limited Warranty (page 52) 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 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.
3. Stop the engine, and turn the fuel valve to the OFF position. This
turns off the fuel flow between the fuel tank and the carburetor.
STORAGE
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