Oxygen levels found at 5,000 ft. are a full 14% less than levels found at sea-level.
As carburetor jets remain fixed, the diminished oxygen in the thin mountain air will burn poorly with the carb's fixed amounts of fuel
. The logical outcome is black smoke from the exhaust
, poor fuel
economy, and significantly reduced power outputs.
High Altitude Adjustments usually include:
- Carburetor adjustment to run “lean”
- Idle adjustment to fun “fast”.
- Use higher octane fuel
From the Honda
Owner’s Manual at:
“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 generator at altitudes
above 5,000 feet (1,500 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.
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 5,000 feet (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 servicing dealer return the
carburetor to original factory specifications.”