High Altitude Operation - Honda HP400 Owner's Manual

High Altitude Operation
At high altitude, the standard air-fuel mixture will be too rich.
Performance will decrease, and fuel consumption will increase. A very rich
mixture will also foul the spark plug and cause hard starting.
High altitude performance can be improved by specific modifications
to the carburetor. If you always operate your power carrier at altitudes above
6,000 feet (1,800 meters), have your servicing dealer perform
this carburetor modification.
Even with carburetor modification, engine horsepower will decrease about
3.5 % for each 1,000 foot (300 meter) increase in altitude. The effect of altitude
on horsepower will be greater than this if no carburetor modification is made.
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 6,000 feet (1,800 meters) with a modified carburetor may
cause the engine to overheat and result in serious engine damage. For
use at low altitudes, have your servicing dealer return the carburetor to
original factory specifications.
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