in a stable position. The float chamber is vented
internally by the vent tube at all times. At curb
idle or when the engine is stopped, the chamber is
also vented by the external vent on top of the
primary fuel bowl on some models. This external
vent provides a release of excess fuel vapors from
the bowl into the engine compartment instead of
into the intake manifold.
|needle which controls the mixture delivered at
idle. Turning the needle out increases the volume
of the mixture by allowing a greater flow of the
|From the idle adjusting needle cham
ber, the fuel goes through a short passage in the
main body and down another passage into the
throttle body. The fuel is discharged into the
throttle bore below the throttle plate.
|B. IDLE SYSTEM - GENERAL INFORMA
TION - These carburetors utilize two identical
idle systems, one for each primary barrel. Since
the two passages function identically, only one side
will be considered. At idle, the normal air pres
sure in the float chamber causes the fuel to flow
through the idle system to the greatly reduced
pressure area below the throttle plate. Fuel flows
from the float chamber through the main jet then
into the small angular but horizontal passage
(idle feed) that leads across to a vertical passage.
|(2) IDLE TRANSFER PASSAGE -During
off-idle operation when the throttle plate is moved
slightly, the fuel flows from the metering body into
the main body passage and then into the throttle
body passage. As the idle transfer slot is exposed
to manifold vacuum, fuel is discharged into the
|As the throttle plate is opened wider
and engine speed increases, the air flow through
the carburetor is also increased. This creates
an increased vacuum in the venturi to bring the
main metering system into operation. The flow
from the idle system tapers off as the main meter
ing system begins discharging fuel. The two
systems are engineered to provide smooth gradual
transition from idle to cruising speeds.
|Fuel flows up this vertical passage (idle
well) past the idle feed restriction. The fuel then
flows through a short horizontal passage and is
mixed with air coming in from the idle air bleed.
This fuel and air mixture flows down another
vertical passage. At the bottom of this passage,
the fuel-air mixture branches in two directions,
one through the idle discharge passage and the
other to the idle transfer passage.
|(3) MODEL - 2300, 2300G - Some appli
cations are as previously described but on other
2300, 2300G applications the idle needles may be
located in the throttle body.
|(1) IDLE DISCHARGE PASSAGE - Fuel
flows past the pointed tip of the idle adjusting
|Three Types Needle and Seat Assemblies|