Honda HRZ216TDA Harmony II Owner's Manual page 45

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 61) does not cover fuel
system damage or engine performance problems resulting from
neglectful storage preparation.
You can extend fuel storage life by adding a fuel stabilizer (page 60)
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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