O.S. Engines 21VZ-B V-Spec - Manual (Page 13)

CARBURETOR CONTROLS
Carburetor Reducer
Needle Valve
Mixture Control Valve
Assembly Screw
Throttle Stop
Screw
Metering Needle
Thermo Insulator
Four adjustable controls are provided on
this carburetor.
The Needle-Valve:
For adjusting the mixture strength when the
throttle is fully open.
The Mixture Control Screw:
For changing the mixture strength at mid
speed and acceleration. (Do not rotate the
screw more than one turn.)
The Metering Needle:
For adjusting the mixture strength at part-
throttle and idling speeds, to obtain steady
idling and smooth acceleration to mid
speeds.
The Throttle Stop Screw:
For setting the minimum idling speed:
NOTE: Readjustment may be necessary,
occasionally to allow for changes in fuel
formula gear ratio or clutch engagement
point.
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