float pontoon is solid and is made of a light, closed-cell
plastic material. This feature gives added bony-'
ancy which allows the
use of a single float to maintain constant
float system (Figure 2) consists of a fuel chamber (float
bowl), a single pontoon float, float hinge pin and retainer
combination, float valve - pull
clip - and
seat, idle vent valve
(some applications), vacuum vent switch valve (some
applications), and internal vents. A plastic filler block
is located in the top of the float chamber over the float
valve to prevent fuel slosh into this area.
most models, a fuel inlet filter is an integral part of the
float bowl, with the filter located behind the fuel inlet nut.
Should the filter become plugged due to excessive dirt or
improper service, a pressure relief spring located behind the
filter element allows fuel pump pressure to force the element off its seat.
This allows fuel to by-pass the filter and
enter the carburetor so the engine will run until the filter
can be serviced.
is very important that the filter be serviced periodically
to prevent dirt from entering the carburetor metering orifices.
float system operates in the following manner:
from the engine fuel pump enters the carburetor fuel
inlet passage. It passes through the filter element, fuel inlet
valve, and on into the float bowl chamber. As the incoming
fuel fills the float bowl to the prescribed level, the float
pontoon rises and forces the fuel inlet valve closed, shutting off fuel
flow. As fuel is used from the float bowl, the
float drops allowing the float valve to open, allowing more fuel
to again fill the bowl. This cycle continues, maintaining
a constant fuel level in the float bowl.
float needle pull clip, fastened to the float needle valve,
hooks over the edge of the float arm at the center as shown
in Figure 2. Its purpose is to assist in lifting the float valve
off its seat whenever fuel level in the float bowl is low.
Do not place pull clip through small
holes in top of float arm. Severe flooding will
are two types of float needle valves used in the Quadrajet
carburetor: One type is diaphragm assisted and the other is the conventional
needle and brass seat.
diaphragm assisted float needle (shown in the right inset Figure 2) is used
primarily with a smaller float and on engines
equipped with high pressure fuel pumps. The needle seat
is a brass insert and is pressed into the bowl fuel inlet channel
below the diaphragm needle tip. The seat is not removable, as the needle
valve tip is of a material which makes seat wear negligible. Care should
be used during servicing
so that the seat is not nicked, scored, or moved. The float valve is factory
staked and tested and should not be
re-staked in the field.