Yamaha RST90K Owner's Manual download pdf (Page 63)

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ESU00157

High altitude adjustments

Operating at high altitude reduces the performance of a

gasoline engine to 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. Follow the Main Jet Setting

chart which is available at a Yamaha dealer carefully.

Proper carburetion adjustments will correct the air/fuel

ratio.

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. They

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 over a high altitude of

900 m (3,000 ft). Consult a Yamaha dealer.

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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Yamaha RST90K Owner's Manual Page 63