Carburetor Modification For High Altitude Operation - Honda HSM1590i Manuel De L'utilisateur

Carburetor Modification for 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.
Operation at an altitude that differs from that at which this engine was
certified, for extended periods of time, may increase emission.
High altitude performance can be improved by specific modifications
to the carburetor. If you always operate your snowblower at altitudes
above 1,500 meters (5,000 feet), have your authorized Honda servicing
dealer perform this carburetor modification.
This engine, when operated at high altitude with the carburetor
modifications for high altitude use, will meet each emission standard
throughout its useful life.
Even with carburetor modification, engine horsepower will decrease
about 3.5 % for each 300 meter (1,000 foot) 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 1,500 meters (5,000 feet) 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.
41