Honda EB2500X Owner's Manual page 25

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 pin ing occurs at a steady engine speed, under
normal load, change % rands of gasoline. If spark knock or pinging
persists, see an authorized Honda generator dealer.
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.
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