4.8
CARBURATION AND FUEL SYSTEM
© Copyright 2011 Polaris Sales Inc.
9923412 - 2012 Sportsman 400/500 and EFI Tractor Service Manual
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.
Carburetor Venting
The carburetor float bowl vent lines supply atmospheric
pressure to the float bowl. The lines must be free of kinks,
restrictions and be properly routed. This allows fuel to flow
in the proper amount and prevents contaminants from
entering the carburetor.
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.
Note: Diagrams are for explanation of theory only, and are not true
representations of Mikini BST carburetor.
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