Storage - Honda EU30is Owner's Manual

Petrol will oxidize and deteriorate in storage. Old petrol will cause hard
starting, and it leaves gum deposits that clog the fuel system. If the petrol in
your generator deteriorates during storage, you may need to have the
carburetor and other fuel system components serviced or replaced.
The length of time that petrol can be left in your fuel tank and carburetor
without causing functional problems will vary with such factors as petrol
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. Fuel deterioration problems may occur after 30 days from
keeping the fuel in the fuel tank, or even less depending on the petrol
formulation in your area.
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