Honda Power Products F220 Manuel De L'utilisateur page 26

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 emissions.
High altitude performance can be improved by specific modifications to
the carburetor. If you always operate your tiller at altitudes above
1,500 meters (5,000 feet), have your 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.
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 (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 specification.
23