Polaris 2001 50 SCRAMBLER, Manual

Page: 67 / 125

FUEL SYSTEM/CARBURETION
3.3
PILOT JET
From idling to low speeds, the fuel supply is metered by the
pilot jet. There are several air bleed openings in the sides
of the pilot jet which reduce the fuel to mist. The number
stamped on the jet is an indication of the amount of fuel in
cc’s which passes through the jet during a one minute inter-
val under a given set of conditions.
PILOT AIR SCREW
The pilot air screw controls the fuel mixture from idle to low
speeds. The tapered tip of the air screw projects into the air
passage leading to the pilot jet air bleeds. By turning the
screw in or out, the cross sectional area of the air passage
is varied, in turn varying the pilot jet air supply and changing
the mixture ratio.
AIR/FUEL MIXTURE RATIO
A carburetor with a piston type throttle valve is also called
a variable venturi type carburetor. In this type of carburetor,
the needle jet and jet needle serve to control a proper air/
fuel mixture ratio at the medium throttle valve opening (be-
tween 1/4 and 3/4 opening). Having the proper needle jet
and jet needle has a major impact on engine performance
at partial load.
The jet needle tapers off at one end and the clearance be-
tween the jet needle and the needle jet increases as the
throttle valve opening gets wider. The air/fuel mixture ratio
is controlled by the height of the “E” ring inserted into one
of the five slots provided in the head of the jet needle. The
chart at right shows the variation of fuel flow based on the
height of the “E” ring.
Pilot Jet
Indicator
Number
Pilot Air Screw
2
3
4
4
3
2
15
50 75 100%
Throttle Valve Opening
E-Clip Position Vs. Fuel Flow