Honda BF5A Owner's Manual page 26

l High attitude operation
At high altitude, the standard carburetor air-fuel mixture will be exces-
sively rich. Performance will decrease, and fuel consumption will increase.
High altitude performance can be improved by installing a smaller diameter
main fuel jet in the carburetor and readjusting the pilot screw. If you always
operate the outboard motor at altitudes higher than 6,000 feet above sea
level, have your authorized Honda Outboard Motor dealer perform these
carburetor modifications.
Even with suitable carburetor jetting, engine horsepower will decrease
approximately 3.5% for each 1,000 foot increase in altitude. The affect of
altitude on 'horsepower will be greater than this if no carburetor
modification is made.
Operation of the outboard motor at an altitude lower than the carburetor
is jetted for may result in reduced performance, overheating, and serious
engine damage caused by an excessively lean air/fuel mixture.
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