High Altitude Operation - Honda HP500H Owner's Manual

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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 specifications to the
carburetor. If you always operate the power carrier at altitude higher
than 1,500 m (5,000 ft) 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 ft) increase in altitude. The
effect of altitude on horsepower will be greater than this if no
carburetor modification is made.
CAUTION:
Operation of the power carrier 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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