Carburetor Modifications for 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 engine
at altitudes above 1,500 meters (5,000 feet), 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
Even with carburetor modification, engine horsepower will
decrease 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.
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 1,500 meters (5,000 feet) 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.
Emission Control System Information
Source of Emissions
The combustion process produces carbon monoxide, oxides of
nitrogen, and hydrocarbons. Control of hydrocarbons and oxides
of nitrogen is very important because, under certain conditions,
they react to form photochemical smog when subjected to
sunlight. Carbon monoxide does not react in the same way, but it
Honda utilizes lean carburetor settings and other systems to
reduce the emissions of carbon monoxide, oxides of nitrogen, and
The U.S. Clean Air Acts and Environment Canada
EPA and Canadian regulations require all manufacturers to furnish
written instructions describing the operation and maintenance of
emission control systems.
The following instructions and procedures must be followed in
order to keep the emissions from your Honda engine within the
Tampering and Altering
Tampering with or altering the emission control system may
increase emissions beyond the legal limit. Among those acts that
constitute tampering are:
Removal or alteration of any part of the intake, fuel, or exhaust
Altering or defeating the governor linkage or speed-adjusting
mechanism to cause the engine to operate outside its design
Problems That May Affect Emissions
If you are aware of any of the following symptoms, have your
engine inspected and repaired by your servicing dealer.
Hard starting or stalling after starting.
Misfiring or backfiring under load.
Black exhaust smoke or high fuel consumption.
The emission control systems on your Honda engine were
designed, built, and certified to conform with EPA and Canadian
emission regulations. We recommend the use of genuine Honda
parts whenever you have maintenance done. These original-
design replacement parts are manufactured to the same standards
as the original parts, so you can be confident of their performance.
The use of replacement parts that are not of the original design
and quality may impair the effectiveness of your emission control
A manufacturer of an aftermarket part assumes the responsibility
that the part will not adversely affect emission performance. The
manufacturer or rebuilder of the part must certify that use of the
part will not result in a failure of the engine to comply with
Follow the maintenance schedule on page . Remember that this
schedule is based on the assumption that your machine will be
used for its designed purpose. Sustained high-load or high-
temperature operation, or use in unusually wet or dusty conditions,
will require more frequent service.