9
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 trimmer 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
NOTICE
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 an authorized Honda servicing
dealer return the carburetor to original factory specifications.
Oxygenated Fuels
Some conventional gasolines are being blended with alcohol or an
ether compound. These gasolines are collectively referred to as
oxygenated fuels. To meet clean air standards, some areas of the
United States and Canada use oxygenated fuels to help reduce
emissions. If you use oxygenated fuel, be sure it is unleaded and
meets the minimum octane rating requirements. Before using an
oxygenated fuel, try to confirm the fuel’s contents. Some states/
provinces require this information to be posted on the pump.
The following are the EPA approved percentages of oxygenates:
If you notice any undesirable operating symptoms, try another service
station or switch to another brand of gasoline.
Fuel system damage or performance problems resulting from the use
of an oxygenated fuel containing more than the percentages of
oxygenates mentioned above are not covered under
the Distributor’s
Limited Warranty
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 is toxic. Honda utilizes
lean carburetor settings and other systems to reduce the emissions of
carbon monoxide, oxides of nitrogen, and hydrocarbons.
The U.S. and California Clean Air Acts
EPA and California 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 emission standards.
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
systems.
• Altering or defeating the governor linkage or speed-adjusting
mechanism to cause the engine to operate outside its design
parameters.
Problems That May Affect Emissions
If you are aware of any of the following symptoms, have your engine
inspected and repaired by an authorized Honda servicing dealer.
• Hard starting or stalling after starting.
• Rough idle.
• Misfiring or backfiring under load.
• Afterburning (backfiring).
• Black exhaust smoke or high fuel consumption.
Replacement Parts
The emission control systems on your Honda engine were designed,
built, and certified to conform with EPA and California 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 system. 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 emission
regulations.
Maintenance
Follow the maintenance schedule on page 4. 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.
LPG Models:
There are no high altitude adjustments for LPG models, however,
engine performance will decrease.
ETHANOL
— (ethyl or grain alcohol) 10% by volume
You may use gasoline containing up to 10% ethanol
by volume. Gasoline containing ethanol may be
marketed under the name Gasohol.
MTBE
— (methyl tertiary butyl ether) 15% by volume
You may use gasoline containing up to 15% MTBE
by volume.
METHANOL
— (methyl or wood alcohol) 5% by volume
You may use gasoline containing up to 5%
methanol by volume as long as it also contains
cosolvents and corrosion inhibitors to protect the
fuel system. Gasoline containing more than 5%
methanol by volume may cause starting and/or
performance problems. It may also damage metal,
rubber, and plastic parts of your fuel system.
LPG Fuels
Use LPG fuel with a propane content of 95% or higher. LPG fueled
engines are certified to operate on LPG only.
