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Periodic maintenance and adjustment
7.
Place the air filter element frame in the
original position, and then install the air
filter case cover by hooking the fasteners.
8.
Install the headlight unit, making sure to
fit the slots on its bottom onto the projec-
tions on its stay.
1
2
1. Slot
2. Projection
9.
Fit the weatherstrip on the headlight unit
into the recess in the top of the air filter
case cover.
1. Weatherstrip
76
10. Install the headlight unit bolts and wind-
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.
RS90P / RS90PLT / RST90PGT: Your snow-
mobile utilizes an electronic fuel injection sys-
tem that delivers the optimal air/fuel ratio
required by the engine. Therefore, the fuel in-
jection system does not need to be adjusted,
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
1
dealer make these adjustments.
shield stay bolts, and then tighten them to
their specified torques.
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)
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