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4.38
CARBURETOR - SPORTSMAN 450
Pilot Screw
The pilot system supplies fuel during engine operation with the
throttle valve closed or slightly opened. The fuel/air mixture is
metered by pilot screw and discharged into the main bore
through the pilot outlet.
Air/Fuel Mixture Ratio
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.
CAUTION
The pilot screw is calibrated at the factory to meet
EPA / CARB regulations for air quality standards
and is sealed with a brass plug to prevent tampering.
Removal of the tamper proof plug is not permitted.
For service purposes, cleaning of the pilot circuit can
be done only by a certified repair shop to ensure air
quality standards are not exceeded.
Pilot Screw Location
Brass Plug Installed
Brass Plug Removed
E-Clip Position vs. Fuel Flow
Throttle Valve Opening
2
3
4
4
3
2
15
50
75
100%