Polaris TX Starfire Owner's Manual page 72

CARBURETORS (Can't.)
PI LOT SYSTEM
The pilot system is designed to deliver gasoline during idling and
low-speed driving.
Fuel for idling is measured by the pilot jet, mixed with the air,
regulated with the air screw, mixed again with the air from the
by-pass, and delivered to the engine through the pi lot outlet.
The concentration of fuel-air mixture for idling is determined
by the air screw. When the air screw is closed, the amount of
air is reduced and the fuel-air mixture is enriched. When the air
screw is opened, the amount of air increases and the fuel-air
mixture is lean.
When the throttle valve opens slightly during low speed driving,
gasoline injects through the by-pass in addition to the fuel-air
mixture from the pilot outlet to secure smooth operation of
the engine. When the throttle valve opens wider, approximately
above 1/8 of the diameter of the main bore, gasoline injects
through the needle jet. The adjustment of the time and amount
of injection from the needle jet is chiefly performed by the
cutaway furnished on the side of the air cleaner of the throttle
valve.
MAIN SYSTEM
The main system is designed for delivering fuel between low
speed driving and high speed driving.
The fuel during the low speed driving is delivered from the
pilot system and the main system. During intermediate speed
driving (the opening of the throttle valve is above 1/4), the
fuel is largely delivered from the main system. The fuel during
intermediate speed driving flows into the needle jet through
the main jet and mixes with the air measured by the air-jet
to make a fine spray of fuel-air mixture of good quality.
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