HONDA HHT31S - Manual (Page 56)

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TECHNICAL & CONSUMER INFORMATION
TECHNICAL INFORMATION
This chapter contains important information about serial number locations, high altitude operation,
oxygenated fuels, and emissions control systems.
Serial Number Locations
There are two serial numbers, one for the trimmer and one for the engine. Record these numbers in
the space provided. You will need to have these numbers available when ordering parts or making
technical or warranty inquiries (page 60).
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.
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.
Engine Serial number: Frame Serial number:
FRAME SERIAL NUMBER
ENGINE
SERIAL
NUMBER
ENGINE
SERIAL
NUMBER
HHT25S
HHT31S
NOTICE