Mikuni Carburetor; Function; Float System - Polaris 340 CLASSIC 2006 Manual

components. The float level is pre-set in the molding and
cannot be adjusted.
WARNING
DO NOT pressurize the fuel system by forcing compressed
air through the fuel tank. Forcing air through the needle and
seat will cause damage and the float/needle & seat assembly
will have to be replaced.
Carburetor Synchronization: Remove the top caps on all
carburetors. In the body of the carburetors, there is a Phillips
head set screw (I) that connects the slide lever to the throttle
lever shaft. The carburetor with the fixed set screw is the base
carburetor (middle carburetor on triples, PTO carburetor on
twins) and the remaining carbs are synchronized to it.
Carburetor synchronization is measured at wide open throttle.
Open the throttle to wide open. The bottom of the slide should
be flush with the top of the throttle bore. If it is not flush,
locate the wide open throttle stop screw (J) and turn it until the
base carburetor is set flush. Loosen the Phillips head set screw
in the remaining carburetor(s). Turn the adjusting nut (K) that
surrounds the set screw until the throttle slide is set the same
as the base carburetor. Tighten all set screws and replace the
top caps making sure gaskets are properly positioned.

MIKUNI CARBURETOR

FUNCTION

The function of a carburetor is to produce a combustible air/
fuel mixture by breaking fuel into tiny particles in the form of
vapor, to mix the fuel with air in a proper ratio, and to deliver
the mixture to the engine. A proper ratio means an ideal air/
fuel mixture which can burn without leaving an excess of fuel
or air. Whether the proper mixture ratio is maintained or not is
the key to efficient engine operation.
The engine of a vehicle is operated under a wide range of
conditions, from idling with the throttle valve remaining
almost closed, to full load or maximum output with the throttle
valve fully opened. In order to meet the requirements for the
proper mixture ratio under these varying conditions, a low
speed fuel system, or pilot system, and a main fuel system are
provided in Mikuni type carburetors. The Mikuni carburetor
has varying operations depending upon varying driving
conditions. It is constructed of a float system, pilot system,
main system, and starter system or initial starting device.

FLOAT SYSTEM

The float system is designed to maintain a constant height of
gasoline during operation. When the fuel flowing from the fuel
pump into the float chamber through the needle valve reaches
the constant fuel level, the floats rise. When the buoyancy of
the float and the fuel pressure of the fuel pump balance, the
needle valve sticks fast to the needle seat, preventing further
delivery of gasoline, thereby holding the standard level of
gasoline.
The fuel level in the bowl assists in controlling the amount of
fuel in the fuel mixture. Too high a level allows more fuel than
necessary to leave the nozzle, enriching the mixture. Too low a
level results in a leaner mixture, since not enough fuel leaves
the nozzle. Therefore, the predetermined fuel level should not
be changed arbitrarily.
CARBURETION
4.7