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0743-084
2. Rotate each fuel mixture screw counterclockwise
the correct number of turns for an initial setting.
Adjusting Air Screws
1. While counting the rotations, carefully rotate the
air screws clockwise until lightly seated.
2. Rotate the air screws counterclockwise the exact
number of rot 1/4 turn from the seated
position as an initial setting.
Adjusting Engine Idle Speed
NOTE: Make engine idle adjustment only after the
engine has reached running temperature. Since
the idle speed screw has not been adjusted, apply
slight throttle pressure to keep the engine running.
Allow engine to warm up for 2-3 minutes.
1. After the engine has been allowed to warm up for
2-3 minutes, fine-tune the idle speed screw until
the tachometer reads 1500 RPM.
2. Test the throttle control lever by compressing and
releasing it several times. The lever must return to
the idle position quickly and completely.
Selecting Carburetor Main Jets
Altitude, temperature, and the use of oxygenated or rac-
ing gasoline affect the carburetion needed for optimum
engine performance. The carburetor main jets must be
changed in conjunction with changes in operating alti-
tude and temperature. As the ambient temperature rises
or as the snowmobile is operated at a higher altitude, the
main jets must be replaced with leaner main jets.
The original equipment (production) main jets are
main jets that may need to be changed (depending
upon the type of gasoline you are using, your operating
altitude, and temperature) following the break-in
period to the proper main jets for the operating condi-
tions. Refer to the Main Jet Chart. It should be noted
that when selecting the proper main jets, it is better to
be too rich rather than too lean. To change carburetor
main jets, use the following procedure:
1. Remove the drain plug and O-ring from the carbu-
retor float chamber and drain the gas into a small
container or shop towels.
735-539B
2. Using the main jet wrench (supplied in the tool
bag), thread the main jet out of the carburetor.
3. Install the new main jet and tighten securely.
4. Install the drain plug and O-ring; then tighten
securely.
5. Repeat steps 1-4 on the other carburetor.
Reed Valves
It is advisable to inspect the reeds for damage or wear
every 7 1/2-10 hours or replace them every year.
CAUTION
Do not force a fuel mixture screw when rotating it clock-
wise; damage to the mixture screw taper may result.
CAUTION
Do not force an air screw when rotating it clockwise;
damage to the air screw will result.
! WARNING
DO NOT operate the snowmobile when any compo-
nent in the throttle system is damaged, frayed, kinked,
worn, or improperly adjusted. If the snowmobile is
operated when the throttle system is not functioning
properly, personal injury could result.
CAUTION
Use only GENUINE Mikuni brass main jets.
CAUTION
A main jet which is too small will cause severe engine
damage.
! WARNING
Whenever any maintenance is performed on the fuel
system, there should be no welding, smoking, open
flames, etc., in the area.
