Air / Fuel Mixture Ratio; Jet Needle; Needle Jet - Polaris PREDATOR 50 2009 Manual

Air / Fuel Mixture Ratio

E-Clip Position vs. Fuel Flow
2
3
4
4
15
Throttle Valve Opening
A carburetor with a slide 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 proper air/fuel mixture
ratio at the medium throttle valve opening (between 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 between 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" clip
inserted into one of the five slots provided in the head of the jet
needle. The previous chart shows the variation of fuel flow
based on the height of the "E" clip.
3
2
50 100%
75

Jet Needle

The jet needle has five adjustment grooves cut into the upper
portion, and is tapered from approximately the middle of the
needle to the lower end. The top is fixed to the center of the
throttle valve by the needle clip, and the tapered end extends into
the needle jet. Fuel flows through the space between the needle
jet and jet needle. This space does not vary until the throttle
reaches the 1/4 open point. At that time the tapered portion of the
needle begins to move out of the jet, affecting fuel flow as the
opening enlarges. If the needle clip is changed from the standard
position to a lower groove, the needle taper starts coming out of
the jet sooner, resulting in a richer mixture. Moving the clip
higher produces a leaner mixture. If the taper is worn due to
vibration, fuel flow may be significantly affected.
Jet Needle
Position#

Needle Jet

The needle jet works in conjunction with the jet needle to
regulate fuel flow rate. An air bleed opening in the side of the
needle jet brings in air measured by the air jet. This air initiates
the mixing and atomizing process inside the needle jet.
Needle Jet
FUEL SYSTEM
Leaner
Richer
Main Jet
4.5
4