Polaris Trail Blazer, Service Manual

Page: 286 / 665

4.21 Polaris Sales Inc. 4/99
FUEL SYSTEM/CARBURETION
Mikuni CV Carb Operation
Float System
Fuel enters the float chamber (3) by
means of the inlet pipe and passage,
through a screen on the back of the inlet
needle seat (4), and around the inlet
needle (2). As the fuel fills the float cham-
ber, the float (1) rises and forces the inlet
needle against the seat, shutting off the
orifice in the seat. When fuel level is up in
float chamber, floats are up and needle
valve remains pushed up against valve
seat. Under this condition, no fuel enters
the float chamber. As the fuel level falls,
floats go down and needle valve unseats
itself to admit fuel into the chamber. In this
manner, the needle valve admits and
shuts off fuel alternately to maintain a
practically constant fuel level inside the
float chamber.
Main System
As throttle valve (1) is opened, engine
speed rises, and this increases negative
pressure in the venturi. Consequently the
vacuum slide (2) moves upward. The fuel
in float chamber (3) is metered by main jet
(4), and the metered fuel enters needle jet
(5), in which it mixes with the air admitted
through main air jet (6) to form an emul-
sion. The emulsified fuel then passes
through the clearance between needle jet
(5) and jet needle (7), and is discharged
into the venturi (A). Mixture proportioning
is accomplished in needle jet (5); the clear-
ance through which the emulsified fuel
must flow is determined ultimately by
throttle position and vacuum slide height.
Inlet
Pipe
1
4
2
3
1
A
5
4
3
6
7
2