Cv Carburetor System Function; Mikuni Cv Carb Operation - Polaris A12MH46AX Service Manual

CARBURATION AND FUEL SYSTEM

CV Carburetor System Function

Carburetor Component Function
Main
System
Components
Float Inlet Pipe,
System Needle and
(Level Seat, Float,
Control) Float Pin
Venting Passages in
Carburetor, Vent
lines
to frame
Starter Choke Lever,
(Choke/ Cable, Plunger,
Enrichment) Return Spring,
Carb Passages
(Starter Jet,
Starter Bleed
Pipe)
Pilot (Idle Pilot Jet/
System) Passage-ways,
Pilot–Mixture
Screw with
Spring Washer
and Sealing O–
Ring, By-pass
Ports (Behind
Throttle Plate),
Pilot Air Jet, Pilot
Outlet, Throttle
Plate
Main Main Jet, Main
System Air Jet, Main Air
Passage,
Needle Jet, Jet
Needle, Vacuum
Slide, Throttle
Plate
4.7
Main Main
Function Affect
Maintains All systems
specified fuel All throttle
level in float ranges
chamber
(carburetor float
bowl)
Supplies All systems
atmospheric All throttle
pressure to float ranges
chamber
Supplies All throttle
additional fuel ranges
air mixture Greatest
necessary for effect at low
cold starting throttle
settings and
idle
Primarily Mainly idle
supplies fuel at to 1/4
idle and low throttle
throttle positions Minimal
effect after
1/2 throttle
Supplies fuel at 1/4 to full
mid–range and throttle
high throttle
settings.
9923412 - 2012 Sportsman 400/500 and EFI Tractor Service Manual
© Copyright 2011 Polaris Sales Inc.

Mikuni CV Carb Operation

The constant velocity
mechanically operated throttle plate and a vacuum
controlled slide valve (vacuum slide). The venturi cross–
sectional area in the carburetor bore is increased or
decreased automatically by the vacuum slide, which
moves according to the amount of negative pressure (less
than atmospheric) present in the venturi.
A diaphragm attached to the top of the vacuum slide is
sealed to the slide and to the carburetor body forming two
chambers. The chamber above the diaphragm is
connected to the venturi area by a drilled orifice in the
center of the vacuum slide. The chamber below the
diaphragm is vented to atmospheric pressure by a
passage on the air box side of the carburetor. A spring,
installed in the center of the vacuum slide, dampens the
slide movement and assists the return of the slide.
Diaphragm
Throttle Plate
= Air Flow
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
pressure in the chamber below the diaphragm forces the
diaphragm upward, raising the slide against spring
pressure.
carburetor incorporates
Low Pressure
From Venturi
Atmospheric
Pressure
Atmospheric
Air inlet
Vacuum
Slide
Venturi
= Low pressure
atmospheric. Atmospheric
a