Honda GX25 Owner's Manual page 17

Carburetor Modifications for High Altitude Operation
At high altitude, the standard carburetor air-fuel mixture will be
too rich. Performance will decrease, and fuel consu m ption will
increase. A very rich mixture will also foul the spark plug and
cause hard starting. O peration at an altitude that differs fro m that
at which this engine was certified, for extended periods of time,
may increase e missions.
High altitude performance can be im proved by specific
m odifications 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 m odification. This engine, when
operated at high altitude with the carburetor m odifications for
high altitude use, will meet each e mission standard throughout its
useful life.
Even with carburetor m odification, 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 m odification is made.
W hen the carburetor has been modified for high altitude operation,
the air-fuel mixture will be too lean for low altitude use. O peration
at altitudes below 1,500 meters (5,000 feet) with a modified
carburetor may cause the engine to overheat and result in serious
engine da mage. For use at low altitudes, have your servicing
dealer return the carburetor to original factory specifications.
Oxygenated Fuels
So me conventional gasolines are being blended with alcohol or an
ether co m pound. These gasolines are collectively referred to as
oxygenated fuels. To meet clean air standards, so me areas of the
U nited States and Canada use oxygenated fuels to help reduce
e missions.
If you use oxygenated fuel, be sure it is unleaded and meets the
minim u m octane rating require ments.
Before using an oxygenated fuel, try to confirm the fuel's contents.
So me states/provinces require this information to be posted on
the pu m p.
The following are the EPA approved percentages of oxygenates:
(ethyl or grain alcohol) 10% by volu me
ETHANOL
You may use gasoline containing up to 10%
ethanol by volu me. G asoline containing
ethanol may be marketed under the na me
G asohol.
(methyl tertiary butyl ether) 15% by volu me
MTBE
You may use gasoline containing up to 15%
M TBE by volu me.
(methyl or wood alcohol) 5% by volu me
METHANOL
You may use gasoline containing up to 5%
methanol by volu me as long as it also
contains cosolvents and corrosion inhibitors
to protect the fuel syste m. G asoline
containing m ore than 5% methanol by
volu me may cause starting and/or
performance proble ms. It may also da mage
metal, rubber, and plastic parts of your fuel
syste m.
If you notice any undesirable operating sy m pto ms, try another
service station or switch to another brand of gasoline.
Fuel syste m da mage or performance proble ms resulting fro m the
use of an oxygenated fuel containing m ore than the percentages
of oxygenates mentioned above are not covered under the
Distributor's Limited W arranty .
Emission Control System Information
Source of Emissions
The co m bustion process produces carbon m onoxide, oxides of
nitrogen, and hydrocarbons. Control of hydrocarbons and oxides
of nitrogen is very im portant because, under certain conditions,
they react to form photoche mical sm og when subjected to
sunlight. Carbon m onoxide does not react in the sa me way, but it
is toxic.
Honda utilizes lean carburetor settings and other syste ms to
reduce the e missions of carbon m onoxide, oxides of nitrogen, and
hydrocarbons.
The U.S., California Clean Air Acts and Environment Canada
EPA, California and Canadian regulations require all
manufacturers to furnish written instructions describing the
operation and maintenance of e mission control syste ms.
The following instructions and procedures m ust be followed in
order to keep the e missions fro m your Honda engine within the
e mission standards.
Tampering and Altering
Ta m pering with or altering the e mission control syste m may
increase e missions beyond the legal limit. A m ong those acts that
constitute ta m pering are:
Re m oval or alteration of any part of the intake, fuel, or exhaust
syste ms.
Altering or defeating the governor linkage or speed-adjusting
mechanism to cause the engine to operate outside its design
para meters.
Problems That May Affect Emissions
If you are a ware of any of the following sy m pto ms, have your
engine inspected and repaired by your servicing dealer.
Hard starting or stalling after starting.
Rough idle.
Misfiring or backfiring under load.
Afterburning (backfiring).
Black exhaust sm oke or high fuel consu m ption.
Replacement Parts
The e mission control syste ms on your Honda engine were
designed, built, and certified to conform with EPA, California and
Canadian e mission regulations. W e reco m mend the use of
genuine Honda parts whenever you have maintenance done.
These original-design replace ment parts are manufactured to the
sa me standards as the original parts, so you can be confident of
their performance. The use of replace ment parts that are not of the
original design and quality may im pair the effectiveness of your
e mission control syste m.
A manufacturer of an aftermarket part assu mes the responsibility
that the part will not adversely affect e mission performance. The
manufacturer or rebuilder of the part m ust certify that use of the
part will not result in a failure of the engine to co m ply with
e mission regulations.
ENGLISH
17