Honda FJ500 Owner's Manual page 66

STORAGE
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 tiller 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 warranty does not cover fuel system damage or engine
performance problems resulting from neglected storage preparation.
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