High Altitude Operation - Honda H3011H Owner's Manual

High Altitude Operation
At high altitude, the standard carburetor air-fuel mixture will be too rich.
Performance will decrease, and fuel consumption will increase. A very rich
fuel mixture may also foul the spark plugs and cause hard starting.
High altitude performance can be improved by installing a smaller diameter
main fuel jet in the carburetor and readjusting the pilot screw. If you
always operate the engine at altitudes higher than 6,000 feet above sea
level, have an authorized Honda riding mower dealer perform this carbu-
retor modification.
Even with carburetor modification, engine horsepower w :II decrease about
3.5% for each 1,000 feet increase in altitude. The effect of altitude on
horsepower will be greater than this if no carburetor modification is made.
Whe,n the carburetor is modified for good high altitude operation, the
air/fuel mixture will be too lean at low altitude. Performance will decrease,
the engine will overheat.
To avoid an excessively lean air/fuel mixture, reinstall the standard main
jet and readjust the pilot screw for operation at altitudes lower than 6,000
feet above sea level.
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