High Altitude Operation - Honda Car engines GX640 Owner's Manual

4. OPERATION
HIGH ALTITUDE OPERATION
At high altitude, the standard carburetor air-fuel mixture will be too
rich. Performance will decrease, and fuel consumption will in-
crease. A very rich mixture will also foul the spark plugs and cause
hard starting.
High altitude performance can be improved by specific modifica-
tions to the carburetor. If you always operate your engine at
altitudes above
1,800
meters (6,000 feet), have your dealer per-
form this carburetor modification.
Even with carburetor modification, engine horsepower will de-
crease 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.
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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 1,800 meters (6,000 feet) with a modified carbure-
tor 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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