Polaris 2012 Sportsman Forest 500 International, Service Manual

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4.9
CARBURATION AND FUEL SYSTEM
© Copyright 2011 Polaris Sales Inc.
9923412 - 2012 Sportsman 400/500 and EFI Tractor Service Manual
Pilot (Idle and Slow) System
This system supplies fuel during engine operation with
throttle valve closed (1) or slightly opened. The 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 venturi.
Consequently the vacuum slide (2) moves upward. The
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
emulsion. The 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.
4
1
6
7
5
2
3
1
2
3
4
5
6
7
A