Fuel / Exhaust
4.21
Mixture Screw Inspection and Adjustment
Carburetor mixture screws pre-adjusted at the factory and usually no adjustment is necessary. Exceptions would
be after cleaning or overhaul, or when minor adjustments are required for altitude. Refer to carburetor specifica-
tions at the beginning of this section and perform the following adjustments.
IMPORTANT: Prior to performing any adjustments to carburetors check the following:
S Verify that no water is present in the fuel system. Check the water trap for presence of water.
S Verify all fuel and vent lines are routed and secured properly.
S Verify all seal and gaskets are in good condition (no air leaks present).
S Check engine compression (see engine section).
S Verify proper fuel flow (i.e. fuel flow through shut off valve passages, tank, lines, and filters).
S Synchronize carburetors; inspect throttle plates (butterfly) for damage.
NOTE: The idle should be set to specification prior to adjusting the mixture screw(s).
1. Locate the low--speed mixture screw(s). Each
carburetor will have a screw.
2. T urn screw clockwise until screw is lightly seated.
CAUTION:
Do not overtighten screw in bore. Damage to needle tip
will occur .
3. Back screw out counter--clockwise as specified in
beginning of chapter.
4. If problem is suspected with adjustment screw ,
remove screw and inspect.
5. Screw tips should not be worn or broke. Replace
mixture screw is either is found.
IDLE SCREW
LOW SPEED SCREW
Damaged Mixture Needle (Bottom)
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