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Periodic maintenance and adjustment
77
10. Install the headlight unit bolts and wind-
shield stay bolts, and then tighten them to
their specified torques.
11. Install the top cover and the shroud.
ESU11911
Carburetors (RST90)
The carburetors are an important part of the
engine and its emission control system, which
require very sophisticated adjustment. There-
fore, carburetor adjustments should be left to
a Yamaha dealer, who has the necessary pro-
fessional knowledge and experience.
ESU13980
High-altitude settings
Operating at high altitude reduces the perfor-
mance of a gasoline engine about 3% for ev-
ery 305 m (1000 ft) of elevation. This is
because there is less air as altitude increases.
Less air means less oxygen available for
combustion.
RS90GT / RS90LTGT / RST90GT: Your
snowmobile utilizes an electronic fuel injec-
tion system that delivers the optimal air/fuel
ratio required by the engine. Therefore, the
fuel injection system does not need to be ad-
justed, even for operation at high altitude.
RST90: Your snowmobile can be adjusted to
overcome most of the problems found in high-
altitude riding. Carburetor adjustments are the
most important. Less air at high altitude
makes the air/fuel ratio too rich, which can
cause poor performance. Common problems
are hard starting, bogging, and plug fouling.
Proper carburetion adjustments will correct
the air/fuel ratio. Be sure to have a Yamaha
dealer make these adjustments.
Remember:
Less air at higher altitude means there is less
horsepower available, even with the optimal
air/fuel ratio. Expect acceleration and top
speed to be reduced at higher altitudes.
To overcome operating with less power at
high altitudes, your snowmobile may also re-
quire different settings for the drive chain
gears and V-belt clutch to avoid poor perfor-
mance and rapid wear. If you plan to operate
your snowmobile at an altitude different from
the area where you bought it, be sure to con-
sult a Yamaha dealer. The dealer can tell you
if there are any changes necessary for the al-
titude where you plan to ride. NOTICE: The
drive chain gears and V-belt clutch should
be adjusted when operating above a high
altitude of 900 m (3000 ft). Consult a
Yamaha dealer.
[ECS00431]
ESU11950
Valve clearance
The valve clearance changes with use, result-
ing in improper air-fuel mixture and/or engine
noise. To prevent this from occurring, the
valve clearance must be adjusted by a
Yamaha dealer at the intervals specified in
the periodic maintenance chart.
ESU13793
Engine oil and oil filter cartridge
The engine oil level should be checked before
each use. In addition, the oil must be changed
and the oil filter cartridge replaced at the inter-
vals specified in the periodic maintenance
and lubrication chart.
WARNING
EWS00370
Engine oil is extremely hot immediately af-
ter the engine is turned off. Coming into
contact with or getting any engine oil on
your clothes could result in burns.
Tightening torques:
Headlight unit bolt:
3.0 Nm (0.30 m·kgf, 2.2 ft·lbf)
Windshield stay bolt:
14 Nm (1.4 m·kgf, 10 ft·lbf)
U8JA11E0.book Page 77 Monday, June 14, 2010 10:22 AM