1935 Cadillac - GM Heritage Center

125
GASOLINE SYSTEM
General Description
The general arrangement of the gasoline system
is practically the same on all cars. The 370-D
and 452-D systems differ slightly, however, as
each of these cars has two carburetors.
The gasoline line from the rear supply tank is
mounted outside of the frame channel where the
air sweeping by tends to cool the gasoline and
thereby prevents the possibility of vapor lock.
Sharp bends and low spots in the fuel line have
also been eliminated by running the line as nearly
straight as possible from the tank to the fuel
pump.
CADILLAC
CARBURETOR
The Cadillac carburetors are of the expanding
air vane type. They are simple in construction
with no thermostats and have only one adjustment,
which controls the mixture by varying the
flow of fuel rather than the air.
The carburetors used on the various Cadillac
models are of the same construction but differ in
size and other minor details. The 370-D and
452-D carburetors are identical with the exception
of the size of the metering pin. Right and left
carburetors also differ in the control levers. The
name plate marking identifies the type of carburetor
; 3 70-D carburetors are Type R-13 and L-13;
452-D carburetors are Type R-14 and L-14.
Otherwise the carburetors on these car models are
fully interchangeable. The carburetor consists
chiefly of two units; namely, the main metering
unit and the auxiliary unit.
The main metering unit consists of a pair of
air valves or vanes, hinged at their lower ends
and opening upwards to admit air to the mixing
chamber. These vanes have fingers which engage
a control aspirating tube, raising it as the vanes
open. This aspirating tube is attached to a spring
loaded hollow stem and piston working in a dashpot,
the piston carrying the fuel metering orifice
in its lower end. An adjustable tapered metering
pin projects into this orifice.
The auxiliary unit combines an auxiliary power
jet, an accelerating pump and a priming passage
for starting. The operation of the auxiliary unit
is controlled by the registering of ports in the
starting sleeve, which line up with passages in the
throttle body. The starting sleeve rotates with
the starting lever (choke lever) and the pump
plunger and piston move downward as the throttle
is opened.
For normal running the fuel enters the carburetor
float bowl through the strainer and float
needle valve and is maintained at constant level
by the float and float needle valve.
Air enters the carburetor through the air inlet
and lifts the vanes as it passes upwards into the
mixing chamber. The weight of these vanes combined
with the pressure exerted by the dashpot
spring causes a partial vacuum to exist in the
mixing chamber, which draws fuel from the
aspirating tube. The quantity of the fuel flowing
is controlled by the tapered metering pin; at idle
speed the vanes are almost closed and the metering
pin almost fills the orifice in the air valve
piston. As the vanes rise to admit more air, the
aspirating tube also rises and the metering orifice
becomes larger due to the taper on the metering
pin. This combination maintains the correct ratio
of fuel and air for average running.
For maximum power at any speed a richer mixture
is required than is necessary for part throttle
running. The power jet supplies the required
extra fuel while the throttle is held open beyond
the point which would give a road speed of about
60 miles per hour. At this throttle position the
pump plunger has travelled downward and has
shut off the air vent to the power jet, therefore,
the suction on the discharge nozzle draws fuel
from the pump cylinder up through the hollow
stem of the pump plunger and through the power
jet into the mixing chamber. At part throttle
positions below 60 miles per" hour road speed this
power jet does not supply fuel since it is vented
to the outside air through the air vent hole in the
upper part of the starting sleeve.
The quantity of fuel drawn from the power jet
is controlled by the air bleed hole in the pump
plunger stem.
For rapid acceleration it is necessary to supply
a momentarily rich mixture. This extra fuel is
supplied by means of the accelerating pump.
A rapid opening of the throttle causes a rapid
downward movement of the pump plunger and
piston, forcing fuel up through the hollow stem
of the pump plunger and out through the discharge
nozzle into the mixing chamber. The fuel
in the pump cylinder cannot escape back into the
float chamber because of the check valve in the
bottom of the pump cylinder.
In general, for steady driving conditions up to
60 miles per hour on level roads, the fuel is all
supplied from the aspirating tube. When the
throttle is opened suddenly an additional charge
of fuel is supplied from the accelerating pump, and
if the throttle is held open as for hard pulling or
high speed, extra fuel continues to flow from the
pump discharge nozzle through the power jet.
All Cadillac cars are equipped with a semi-automatic
choke, which permits a more efficient
choking of the carburetor during the warming up