Cadillac 54-6219 1954 Shop Manual page 234

ENGH'IE FUEL AND EXHAUST
vent veive spring, and idle vent valve. When the
throttle vaives ore closed, the actuating lever ron
Lads the spring loaded vent valve and holds it
open. 'Oils permits vapore from the float kiwi to
be vented to 'he atmosphere. As the throttle
va;vcis are opened, the idls ventvalve spring closes
the vent valve thus eliminating the atmospheric
vent and returning the carburetor tu an Internal
bshsnce.
A cored passage in thin bowl casting links the
Pr irna ry and seconds ry lisa
t
bowls toga
t
lie r. in
this way any abnormal rise in fuel level on one
side will rand to be absorbed by the other, and
should not seriously disrupt die operation of the
engine. This passage also equelizes vo],Jr 2res
-
sLices between ±e two howls.
Idle Circuits
At small throttle openings, the vacuum created
at the main discharge nozzles is not peat enough
to cause fuel
to
flow from the nozzles. Additional
systems are provided
to
supply the proper nrixture
ratios required thruaghrut the idling range. 'l'[iese
circuits are shown in Fig. 12-2.
A fixed idle system is provided ±n the pri';iary
throttle bores which is supplied with mel from the
sewndary side or the carburetor. Tue secondary
idle fuel is drawn from ihe float bowl through the
ma n metering jets into the
fIle I
we LI
Ii
tho borro ni
of the secondary float bowl. It then passes through
the calibrated restriction in the end of esch idle
tube. The fuel is then drawii up through the idle
tube, es bled at the idle air bleeds, passe.s through
other calibrated restrictions, and is again bled by
additional calibrated air bleeds. 'flds iliixture is
drawn rhiroughi thin channel In the fiosr bowl around
the secondary throttle body bores, is further bled
by the lower idle air bleeds, and is discharged from
the throttle body idleorifices in the primary throttle
bores. As the throttle is opened, the vacuum acting
on the fixed idle discharge boles decreases very
rapidly. These discharge holes, diereluru, stop
feeding fuel in tile off-Idle range.
In addihion, an adjusts hle idle system is provided
in the- primary side or the carburetor. This syetem
provides the balance of fuel required for nuroml
curb idle as sell is that requIred for operstion in
tIle off-idle range. The primary idie fuel is drs,sa.
from the float bowl through the main metering
jets into the fuel well in the bottom of the primary
floar bowl. It then passes through die calIbrated
idle tube restrictions and idle tubes. Air joins this
fuel at the calibrated air bleed and the niixture
passes through a calibrated restriction sod then
through :',;e float bowl idle chaimel, is further bled
at the Lower idlesirhleeds and upper idle holes, and
is discharged from the primary throttle body needle
holes As the throttle valves are opened. the bleed
S ICON BAR V
SIDE
Fig, b2-2 Rocheste, Cotboreter Idle ciroih