Periodic maintenance and adjustment
70
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.
ESU11912
Carburetors (RST90)
The carburetors are an important part of the
engine and its emission control system,
which require very sophisticated adjustment.
Therefore, carburetor adjustments should be
left to a Yamaha dealer, who has the neces-
sary professional knowledge and experience.
ESU13981
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.
RST90TF / RST90TFL / RST90TFY: 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 alti-
tude 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.
[ECS00432]
ESU11951
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.
1. Weatherstrip
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)
1
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