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4.39
CARBURETOR - SPORTSMAN 450
4
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.
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.
Throttle Opening vs. Fuel Flow
In a full throttle condition the cross sectioned area between 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.
Carburetor Disassembly – Mikuni CV
Use the following disassembly, assembly, and inspection
techniques to service a CV carburetor.
1. Remove carburetor diaphragm chamber cover with a
ratchet style screwdriver. DO NOT use an impact driver to
remove the screws or carburetor may be permanently
damaged.
2. Remove float bowl. Remove the float pin screw. The float
Leaner
Richer
Position#
Jet Needle
Needle Jet
Main Jet
Closed
Throttle
One-half
Throttle
Full
Throttle
Small
Clearance
Medium
Clearance
Large
Clearance