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4.36
CARBURETOR - SPORTSMAN 450
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.
Starter System (Choke or Enrichment)
When the choke cable (1) is activated, the starter plunger (5) is
lifted off the seat.
Fuel is drawn into the starter circuit from the float chamber (2)
through the starter jet (3). Starter jet meters this fuel, which then
flows into starter pipe (4) and mixes with the air (7) coming from
the float chamber. The mixture, rich in fuel content, reaches
starter plunger and mixes again with the air coming through a
passage (8) extending from underneath the diaphragm. The rich
fuel/air mixture for starting is discharged through starter outlet
(6) in the main bore.
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).
Note: Diagrams are for explanation of theory only, and are not true
representations of Mikini BST carburetor.
1
2
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4
5
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8
4
1
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7
5
2
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