Adjusting The High-Altitude Settings; Adjusting The Valve Clearance - Yamaha RS90NL Owner's Manual

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Adjusting the high-altitude settings

Operating at high altitude reduces the performance of a
gasoline engine about 3% for every 305 m (1,000 ft) of
elevation. This is because there is less air as altitude
increases. Less air means less oxygen available for com-
bustion.
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 adjust-
ments 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 proper carburetion.
Expect acceleration and top speed to be reduced at
higher altitudes.
To overcome operating with less power at high altitudes,
your snowmobile may also require different settings for
the drive chain gears and V-belt clutch to avoid poor per-
formance and rapid wear. If you plan to operate your
snowmobile at an altitude different from the area where
you bought it, be sure to consult a Yamaha dealer. The
dealer can tell you if there are any changes necessary
for the altitude where you plan to ride.
CAUTION :
@
The drive chain gears and V-belt clutch should be
adjusted when operating above a high altitude of
900 m (3,000 ft). Consult a Yamaha dealer.
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ESU00348

Adjusting the valve clearance

The valve clearance changes with use, resulting 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 peri-
odic maintenance chart.
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