Polaris 2007 Sportsman 450 EFI, Service Manual

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4.37
CARBURETOR - SPORTSMAN 450
4
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.
Float System
Fuel enters the float chamber (3) by means of the inlet pipe and
passage, through a screen on the back of the inlet needle seat (4),
and around the inlet needle (2). As the fuel fills the float
chamber, the float (1) rises and forces the inlet needle against the
seat, shutting off the orifice in the seat. When fuel level is up in
float chamber, floats are up and needle valve remains pushed up
against valve seat. Under this condition, no fuel enters the float
chamber. As the fuel level falls, floats go down and needle valve
unseats itself to allow fuel into the chamber. In this manner, the
needle valve releases and shuts off fuel alternately to maintain
a constant fuel level inside the float chamber.
1
2
3
4
5
6
7
A
Inlet
Pipe
1
2
3
4