Honda BF5A Owner's Manual page 13

Recommended fuel
Your engine is designed to use any gasoline that has a pump octane
number (R +M)/2 of 86 or higher, or that has a research octane number of
91 or higher. Gasoline pumps at service station normally display the pump
octane number.
We recommend that you use unleaded fuel because it produces fewer
engine and spark plug deposits
and
extends the life of exhaust system
components.
Never use stale or contaminated gasoline or an oil/gasoline mixture. Avoid
getting dirt, dust or water in the fuel tank. Use of a lower octane gasoline
can cause persistent "pinging" or heavy "spark knock" (a metallic rapping
noise) which, if severe, can lead to engine damage.
(1
If "spark knock" or "pinging"
occurs at a steady engine speed under
normal load, change brands of gasoline. If spark knock or pinging persists,
consult your authorized Honda dealer. Failure to do so is considered
misusk and damage caused by misuse is not covered by Honda's Limited
Warranty.
Occasionally you may experience light spark knock while operating under
heavy loads. This is no cause for concern, it simply means your engine is
operating efficiently.
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.
NOTE:
l
Fuel system damage or engine performance problems resulting from the
use of fuels that contain alcohol is not covered under the warranty.
Honda cannot endorse the use of fuels containing methanol since
evidence of their suitability is as yet incomplete.
l
Before buying fuel from an unfamiliar station, try to find out the fuel
contains alcohol, if it does, confirm 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.
11