Honda HSS760A Manuel De L'utilisateur page 40

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 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 snow thrower at altitudes
above 1,500 meters, have your dealer perform this carburetor
modification.
Even with carburetor modification, engine horsepower will decrease
about 3.5% for each 300 meter increase in altitude. The effect of
altitude on horsepower will be greater than this if no carburetor
modification is made.
CAUTION:
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 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 your dealer return the carburetor to
original factory specifications.
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