Fuel Recommendations - Honda HA4118H38A Owner's Manual

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Even with carburetor modification, engine horsepower will decrease
about 3.5% for each 1 ,OOO-foot (300-meter) increase in altitude. The
effect of altitude on horsepower will be greater than this if no
carburetor modification is made.
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When the carburetor has been modified for high altitude operation, the
air-fuel mixture will be too lean for low altitude use. Operation at
altitudes below 5,000 feet (1,500 meters) with a modified carburetor
may cause the engine to overheat and result in serious engine
damage. For use at low altitudes, have an authorized Honda lawn
tractor dealer return the carburetor to original factory specification.
Fuel Recommendations
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 plug deposits and extends
exhaust system life.
Never use stale or contaminated gasoline or an 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 lawn tractor dealer.
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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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