Honda SPORTRAX 250EX 2007, Owner'S Manual, Page: 190 / 229

181
High Altitude Carburetor Adjustment
Technical Information
When the carburetor has been modif ied f or high altitude operation, the
air-f uel mixture will be too lean f or low altitude use. Operation at
altitudes below 5,000 f eet (1,500 meters) with a modif ied 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 f actory specif ications.
High altitude performance can be improved by specific modifications to
the carburetor. If you always operate your engine at altitudes above
6,500 feet (2,000 meters), 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 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.
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.
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