Honda EG5000X Owner's Manual page 23

We recommend unleaded gasoline because it produces fewer engine and
spark plug deposits and extends exhaust system life.
Never use stale or contaminated gasoline or oil/gasoline mixture. Avoid
getting dirt or water in the fuel tank.
Occasionally you may hear light "spark knock' or "pinging" (metallic rapping
noise) while operating under heavy loads. This is no cause for concern.
If spark knock or pinging occurs at a steady engine speed, under normal
load, change brands of gasoline. If spark knock or pinging persists, see an
authorized Honda generator dealer.
-1 Running the engine with persistent spark knock or
pinging can cause engine damage.
Running the engine with persistent spark knock or pinging is misuse, and
the Distributor's Limited Warranty does not cover parts damaged by misuse.
Oxygenated Fuels
Some gasolines are being blended with alcohol or an ether compound to
increase the octane. These gasolines are collectively referred to as oxygenated
fuels. Some areas of the United States use oxygenated fuels to help meet
clean air standards.
If you use an oxygenated fuel, be sure its pump octane rating is 86 or higher.
Ethanol (ethyl or grain alcohol)
Gasoline containing more than 10% ethanol by volume may cause starting
and/or performance problems. Gasoline containing ethanol may be
marketed under the name "Gasohol".
Methanol (methyl or wood alcohol)
Gasoline containing methanol must contain cosolvents and corrosion
inhibitors to protect the fuel system. Gasoline containing more than 5%
methanol by volume may cause starting and/or performance problems and
may damage metal, rubber and plastic parts of your fuel system.
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