Buick LeSabre 1965 Service Manual page 108

3 - 3 2 2-BARREL ROCHESTER ENGINE FUEL A N D EXHAUST SYSTEMS
NEEDLE SEAT-
FLOAT NEE
FLOAT TANG-
NEEDLE PULL "CLIP
FLOAT
Figure 3-27—Float System
pump, fast idle, choke, choke rod
and choke unloader adjustments
only.
Incorporated in the Rochester
Model 2GC carburetor are six
basic systems. They are Float,
Low Speed, Main Metering, Pow-
er, Accelerating and Choke sys-
tems. The following explanation
and illustrations show that each
system operates to provide effi-
cient carburetion through all
operating conditions.
b. Operation of Float System
The float system controls the
level of the fuel in the carburetor
fuel bowl. Fuel level is very im-
portant because it must be main-
tained to give proper metering
through all operating ranges.
Fuel e n t e r i n g the carburetor
must first pass through the inlet
screen, by the inlet needle seat,
then past the float needle, into the
float bowl; flow continues until the
fuel level raises the float to a
position where it closes the float
valve. As fuel is used from the
carburetor bowl the float drops,
moving the float needle off its
seat and replenishing the fuel in
the bowl, thereby keeping the fuel
level constant. See Figure 3-27.
A float tang located at the rear of
the float arm between the float
hangers prevents the float assem-
bly from moving too far down-
ward, but a l l o w s the f l o a t
a s s e m b l y to move down far
enough for maximum fuel flow
into the carburetor bowl. A float
needle pull clip connecting the
float arm to the needle valve
keeps the needle from sticking
closed in the seat, which may be
caused by dirt or gum formation.
An external vent located on the
top of the carburetor air horn
vents any fuel vapors which may
form in the float bowl to the out-
side atmosphere during periods
of hot engine operation. This
helps prevent poor hot engine
idling and hard hot e n g i n e
starting.
c. Operation of Idle
(Low Speed) System
During engine idle operation, air
flow through the carburetor ven-
turi is very low and is not great
enough to cause fuel to flow from
the main d i s c h a r g e nozzles.
Therefore, the idle system is
used to provide the proper mix-
ture ratios required during idle
IDLE AIR BLEED
IDLE AIR BLEED
IDLE TUBE-
MAIN
METERING-
JETS
ADJUSTMENT NEEDLES
IDLE NEEDLE HOLE
IDLE
RESTRICTION
LOWER
IDLE RESTRICTION
O F F - I D L E
DISCHARGE PORT
THROTTLE VALVE
Figure 3-28—Low Speed System