Polaris TX Starfire Owner's Manual page 73

CARBURETORS (Can't.)
The point of the jet needle is tapered to adjust the flow of fuel-
air mixture in accordance with the opening of the throttle
valve. During high speed driving (the opening of the throttle
valve is above 3/4), the fuel is measured by the main jet and
mixed with the air measured by the air jet to make a fine spray
of fuel-air mixture of good quality for delivery to the engine.
ADJUSTMENTS
When the engine has dual carburetors, it is the prerequisite for
full engine performance to maintain the equal operation of
each carburetor. The following items should be followed
cautiously and accurately.
ADJUSTMENT OF THROTTLE CABLE
With your eye or plug gauge, adjust the opening of each
throttle valve with the throttle cable attached and the throttle
open. With your eye, you can adjust accurately by matching
the corner of the cutaway of the throttle valve with the upper
surface of the main bore. After adjustment, be sure to fasten
the cable adjuster lock nuts as well as the starter wire.
ADJUSTMENT OF IDLING AND SYNCHRONIZATION
(a) Set the air screw of each carburetor at the standard
return number and then fasten the throttle stop screw of each
carburetor evenly, setting the number at about 1,000 RPM
which is a little higher than normal idling speed.
(b) Warm up the engine completely.
(c) Find out and set the position where the number of RPMs
of the engine becomes maximum by opening or closing the air
screws one by one about 1/2 each time. In this case, be sure to
use a tachometer.
(d) Return each screw of the throttle valve evenly and set at
the normal number of rotations of idling.
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