Honda H5518H Owner's Manual page 33

Fuel recommendation
Use unleaded gasoline with a pump octane rating of 86 or higher.
This engine is certified to operate on unleaded gasoline.
Unleaded gasoline produces fewer engine and spark plugs 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
loadchange brands of gasoline. If spark knock or pinging persistssee an
authorized Honda generator dealer.
INOTICE] Running the engine with persistent spark knock or pinging
can cause engine damage.
Running the engine with persistent spark knock or pinging is considered
misuse,and the Distributor's Limited Warranty does not cover parts damaged
by misuse.
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