John Deere AC1-CG16H - Manual (Page 19)

Installation
Operator’s Manual 9
HIGH AlTITude
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
unit at altitudes above 5,000 feet (,500 meters), have your
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 .5% for each ,000-foot (00-meter)
increase in altitude. The effect of altitude on horsepower will
be greater than this if no carburetor modification is made.
NOTE: 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.