Kohler N.A.M.P 6000 Operation Instruction Manual page 13

OPERATIONS
Use unleaded gasoline with a pump octane rating of 86 or higher. This engine is certi-
fied to operate on unleaded gasoline.
Unleaded gasoline produces fewer engine and spark plug deposits and extends ex-
haust 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 gen-erator
dealer.
Running the engine with persistent spark knock or pinging is misuse, and the Distrib-
utor's Limited Warranty does not cover parts damaged by misuse.
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