High Altitude Operation - Honda WB20XT Manual

High altitude operation

At high altitude, the standard carburetor air-fuel mixture will be
excessively rich. Performance will decrease, and fuel consumption will
increase.
High altitude performance can be improved by specific modifications
to the carburetor. If you always operate the pump at altitudes higher
than 1,500 m (5,000 feet) above sea level, have your authorized Honda
dealer perform these carburetor modifications.
Even with suitable carburetor jetting, engine horsepower will decrease
approximately 3.5 % for each 300 m (1,000 foot) increase in altitude.
The effect of altitude on horsepower will be greater than this if no
carburetor modification is made.
Operation of the pump at an altitude lower than the carburetor is
jetted for may result in reduced performance, overheating, and
serious engine damage caused by an excessively lean air/fuel mixture.
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