Polaris 120 XC Rider's Safety Manual And Owner's Operation And Maintenance Manual page 40

OPERATION
Carburetion
Proper carburetor adjustment is critical, since a mixture too lean (too much air, too
little fuel) will result in overheating of the combustion chamber causing pre-ignition
of the fuel. This results in piston burning, bearing failure, or complete engine fail-
ure. A lean mixture can be the result of fuel line restrictions, foreign matter in the
carburetor, etc.
A mixture too rich (too much fuel, too little air) is also unfavorable because it can
foul plugs and cause generally poor engine performance.
All carburetors have been pre-set at the factory for adequate fuel supply. Higher
altitude operation may require different adjustment and settings.
WARNING
Carburetor adjustments must be performed by your dealer, since mistakes can
result in possible operator safety hazards as well as serious engine damage.
Remember, correct setup provides engine RPM within its given power band at full
throttle settings and also provides maximum efficiency and operation at all other
throttle openings. Your dealer has the training and tools required to perform any
adjustments for you.
A--22