Pilot System (Idle And Slow Speed) - Polaris Ranger 500 2x4 2007 Service Manual

Carburetor Operation Cont'd
When the throttle plate is opened and engine speed begins to
increase, the pressure in the venturi (and therefore in the
chamber above the diaphragm) becomes significantly lower
than atmospheric. Atmospheric pressure in the chamber below
the diaphragm forces the diaphragm upward, raising the slide
against spring pressure. When the pressure above and below the
diaphragm are nearly equal, the slide moves downward under
spring pressure. Raising or lowering the slide increases or
decreases the cross sectional area in the venturi, and therefore
the air velocity in the venturi is kept relatively constant. This
provides improved fuel atomization and optimum fuel/air ratio.
Diaphragm
Throttle
Plate
= Air Flow
Note: Diagrams are for explanation of theory only, and are not true
representations of Mikini BST carburetor.
Low Pressure
From Venturi
Vacuum
Slide
From
Air Box
Venturi
= Low Pressure
CARBURETION SYSTEM

Pilot System (Idle and Slow Speed)

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).
4
1
6
7
5
2
3
4
4.7