2008 Polaris ATV Sportsman 300 400 H.O. Service Manual, Page 100Get this manual
FUEL SYSTEM Pilot (Idle and Slow) System
This system supplies fuel during engine operation with throttle valve closed (1) or slightly openedThe fuel from float chamber (2) is metered by pilot jet (3) where it mixes with air coming in through pilot air jet (4)The mixture then goes up through pilot passage to pilot screw (5)A part of the mixture is discharged into the main bore out of bypass ports (6)The remainder is then metered by pilot screw and discharged into the main bore through pilot outlet (7)
Main System
As throttle valve (1) is opened, engine speed rises, and this increases negative pressure in the venturiConsequently the vacuum slide (2) moves upwardThe fuel in float chamber (3) is metered by main jet (4), and the metered fuel enters needle jet (5), in which it mixes with the air admitted through main air jet (6) to form an emulsionThe emulsified fuel then passes through the clearance between needle jet (5) and jet needle (7), and is discharged into the venturi (A)Mixture proportioning is accomplished in needle jet (5); the clearance through which the emulsified fuel must flow is determined ultimately by throttle position and vacuum slide height