'61HN252' by American Honda Motor Co. - Page 132 of 540
http://services.honda.com/ServiceManual/SVC_MNL/61HN253/61HN2...
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3/9/2008 10:46 PM
[2005-2008] [TRX500 FA/FGA]
FUEL SYSTEM
HIGH ALTITUDE ADJUSTMENT
(except U type)
At high altitude, the standard carburetor air-fuel
mixture will be too rich. Performance will decrease,
and fuel consumption will increase. A very rich mix-
ture 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 spe-
cific modifications to the carburetor. If your cus-
tomer always operates the ATV at altitudes above
6,500 feet (2,000 meters), you should perform this
carburetor modification.
Even with carburetor modification, engine horse-
power will decrease about 3.5% for each 1,000-foot
(300-meter) increase in altitude. The effect of alti-
tude on horsepower will be greater than this if no
carburetor modification is made.
This engine, when operated at high altitude with the
carburetor modifications for high altitude use, will
meet each emission standard throughout its useful
life.
The high altitude carburetor adjustment is per-
formed as follows:
Remove the carburetor
(page 5-6)
and the float
chamber.
Replace the standard main jet with the high altitude
O-RING
PILOT SCREW
MAIN JET
type.
HIGH ALTITUDE MAIN JET: # 158
Check that the O-ring on the float chamber is in
good condition and replace it with a new one if
necessary.
Install the float chamber and the carburetor.
Screw in the pilot screw the specified number of
turns from the factory preset position using the spe-
cial tool.
TOOL:
Pilot screw wrench 07KMA-MN90101 or
07KMA-MN9A100 (U.S.A.only)
HIGH ALTITUDE PILOT SCREW OPENING:
1/4 turn in from initial opening
Start the engine and warm it up.
Adjust the idle speed at high altitude with the throt-
tle stop screw to ensure proper high altitude opera-
tion.
IDLE SPEED: 1,400 ± 100 rpm (min
-1
)
when the carburetor has been modified for high alti-
tude operation, the air-fuel mixture will be too lean
for low altitude use. Operation at altitudes below
5,000 feet (1,500 m) with a modified carburetor may
THROTTLE STOP SCREW
cause the engine overheat, resulting in serious
engine damage and increased exhaust emissions.
5-20
