Jet Needle; Needle Jet; Throttle Opening Vs. Fuel Flow - Polaris Magnum 2x4 Service Manual

Polaris atv and light utility vehicle service manual

Table of Contents

FUEL SYSTEM/CARBURETION

Component Functions

The jet needle has five adjustment grooves cut into the up-

per 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

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 pro-

duces a leaner mixture. If the taper is worn due to vibration,

fuel flow may be Significantly affected.

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. Mixing is augmented by a projection at the needle jet

outlet, called the primary choke. The letter number code

stamped on the jet indicates jet inside diameter.

Throttle Opening

In a full throttle condition the cross sectioned area be-

tween the jet needle and the needle jet is larger than

the cross sectioned area of the main jet. The main jet

therefore has greater control over fuel flow.

Polaris Industries Inc.

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