Carburetor Venting; Mikuni Cv Carb Operation - Polaris Hawkeye Repair Manual

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.

MIKUNI CV CARB OPERATION

The constant velocity carburetor incorporates a mechani-
cally operated throttle plate and a vacuum controlled slide
valve (vacuum slide). The venturi cross–sectional area in
the carburetor bore is increased or decreased automati-
cally 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
- www.instant-manuals.com -
Low Pressure
From Venturi
Atmospheric
Pressure
Atmospheric
Air inlet
Vacuum
Slide
Venturi
= Low pressure
FUEL SYSTEM / CARBURETION
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. 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
atomization and optimum fuel/air ratio.
Note: Diagrams are for explanation of theory only, and are not true
representations of Mikini BST carburetor.
atmospheric. Atmospheric
provides improved fuel
4.7