FUEL SYSTEM/CARBURETION
3.5
Float
Guide
Pin
Needle Valve
Float Arm
Float
Fuel Supply
Constant
Fuel Level
Idle Adjustment
Screw
General Carburetor Representation
This 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.
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 these type of carburetors.
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 seals the orifice in the needle seat,
preventing further fuel delivery, and the level of fuel in
the bowl remains relatively constant.
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.
PILOT JET
From idling to low speeds, the fuel supply is metered
by the pilot jet. There are several air bleed openings
in the sides of the pilot jet which reduce the fuel to
mist. The number stamped on the jet is an indication
of the amount of fuel in cc’s which passes through the
jet during a one minute interval under a given set of
conditions.
Pilot Jet
Indicator
Number
17.5
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