Honda WH15X Owner's Manual page 15

Gasoline spoils very quickly depending on factors such as light
exposure, temperature and time.
In worst cases, gasoline can be contaminated within 30 days.
Using contaminated gasoline can seriously damage the engine
(clogged carburetor, stuck valve).
Such damage due to spoiled fuel is disallowed from coverage by the
warranty.
To avoid this please strictly follow these recommendations:
Only use specified gasoline (see page
To slow deterioration, keep gasoline in a certified fuel container.
If long storage (more than 30 days) is foreseen, drain fuel tank and
carburetor (see page
Gasolines containing alcohol
If you decide to use a gasoline containing alcohol (gasohol), be sure
it's octane rating is at least as high as that recommended by Honda.
There are two types of ''gasohol'': one containing ethanol, and the
other containing methanol. Do not use gasohol that contains more
than 10% ethanol. Do not use gasoline containing methanol (methyl
or wood alcohol) that does not also contain cosolvents and corrosion
inhibitors for methanol. Never use gasoline containing more than 5%
methanol, even if it has cosolvents and corrosion inhibitors.
Fuel system damage or engine performance problems resulting
from the use of gasoline that contains alcohol is not covered under
the warranty.
Honda cannot endorse the use of gasoline containing methanol
since evidence of its suitability is as yet incomplete.
Before buying gasoline from an unfamiliar station, first determine if
the gasoline contains alcohol, if it does, find out the type and
percentage of alcohol used.
If you notice any undesirable operating symptoms while using a
gasoline that contains alcohol, or one that you think contains
alcohol, switch to a gasoline that you know does not contain alcohol.
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