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3-2 DISASSEMBLY, REASSEMBLY, INSPECTION, AND MAINTENANCE
Carburetor
Construction and Function
The function of a carburetor is to mix fuel and air by applying the
principle of an atomizer, thus creating an appropriate air-fuel mixture in
accordance with load fluctuations. The major functions of a carburetor
consist of the following four systems.
Pilot System
The function of this system is to supply fuel during the idling and the
low-speed, light-load operating conditions.
The fuel that is regulated by the pilot jet mixes with the air that is
regulated by the pilot air jet, and the resulting mixture is supplied via
the pilot port and bypass port to the engine.
The fuel that is used during idling is supplied primarily via the pilot
port.
A: Pilot Jet
B: Pilot Air Jet (Body Jet)
C: Pilot Port
D: Bypass Port
E: Pilot Screw
F: Pilot Port
Main system
The function of this system is to supply fuel during medium- to high-
speed, high-load operating conditions. Fuel is regulated by the main jet
and flows through the main nozzle.
The air that is regulated by the main air jet intermixes with the fuel
via the bleed hole of the main nozzle, and is discharged into the venturi
in an emulsion form (in which the liquid is intermixed with air bubbles).
In the venturi, the airflow from the air cleaner causes the fuel to
become atomized, and the resulting air-fuel mixture is fed into the
cylinder.
Choke System
Closing the choke valve decreases the volume of air intake and
increases the intake vacuum during the intake stroke. As a result, a
greater volume of fuel than normal is discharged from the pilot and
main systems to facilitate the starting of a cold engine.
Float System
The function of the float is to maintain the fuel in the float chamber
of the carburetor at a constant level so that the proper amount of fuel
can be supplied to the engine.
Setting the fuel level in the float chamber to low makes it more difficult
for the carburetor to draw the fuel up to the venturi, resulting in a leaner
air-fuel mixture.
Setting the fuel level to high increases the volume of fuel that is drawn
up to the venturi, resulting in a richer air-fuel mixture
A: Main Jet
B: Main Nozzle
C: Main Air Jet (body jet)
D: Chocke Valve
E: Throttle Valve
F: Float Hinge Pin