Snowmobile Polaris High Performance (2001 year). Manual - part 35
CARBURETION
3.15
Function
The function of a carburetor is to produce a com-
bustible 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 op-
eration.
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 condi-
tions, a low speed fuel system, or pilot system,
and a main fuel system are provided in Mikuni VM
type carburetors.
The Mikuni carburetor has varying operations de-
pending upon varying driving conditions. It is
constructed of a float system, pilot system, main
system, and starter system or initial starting de-
vice.
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 re-
sults in a leaner mixture, since not enough fuel
leaves the nozzle. Therefore, the predetermined
fuel level should not be changed arbitrarily.
Float Guide Pin
Needle Valve
Float Arm
Float