2003 Polaris Scrambler 50-90 Sportsman 90 Predator 90 Service Manual, Page 60Get this manual
FUEL SYSTEMCARBURETION
AIR SCREW
The air screw controls the fuel mixture from idle to low speedsThe tapered tip of the air screw projects into the air passage leading to the pilot jet air bleedsBy 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
throttle valve opening (between 14 and 34 opening)Having the proper needle jet and jet needle has major impact on engine performance at partial loadThe 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 widerThe airfuel 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 needleThe previous chart shows the variation of fuel flow based on the height of the "E" clip
Air Screw
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 endThe top is fixed to the center of the throttle valve by the needle clip, and the tapered end extends into the needle jetFuel flows through the space between the needle jet and jet needleThis space does not vary until the throttle reaches the 14 open pointAt that time the tapered portion of the needle begins to move out of the jet, affecting fuel flow as the opening enlargesIf the needle clip is changed from the standard position to lower groove, the needle taper starts coming out of the jet sooner, resulting in richer mixtureMoving the clip higher produces leaner mixtureIf the taper is worn due to vibration, fuel flow may be significantly affectedJet Needle