Honda H3011H Owner's Manual page 24

IMPORTANT NoT'CE 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.
Occasionally you may hear light spark knock while operating under heavy
loads. This is no cause for concern. It simply means your engine is
operating efficiently.
We recommend unleaded fuel because it produces fewer engine and spark
plug deposits and extends the exhaust system life.
Never use stale or contaminated gasoline or an oil/gasoline mixture. Avoid
getting dirt or water in the fuel tank.
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