1917 Cadillac - GM Heritage Center

48 ADJUSTMENTS
CARBURETOR
ADJUSTMENT OF CARBURETOR
The carburetor should not be tampered with unless it needs adjustment.
Good carburetor action cannot be expected until the' motor is thoroughly
warmed up. This is particularly true during cold weather. Imperfect carburetor
action while the engine is cold does not indicate that the carburetor
requires adjustment and carburetor adjustment should not be made under these
conditions.
Before changing any of the carburetor adjustments be sure it is the carburetor
which requires attention. It is possible that the ignition system
requires adjustment.
Before making any carburetor adjustments be sure that the points on the
spark plugs are .028 inches apart, that the spark plug cores are clean, that
the timer is properly set and that the timer contact points are clean and in
proper adjustment. In fact, see that the entire ignition system is in good
working order.
When it is certain
that the carburetor requires
adjusting, proceed
as follows:
Open the throttle
about two inches on
the sector at the steering
wheel. Place the
spark lever in the
"Driving Range" on
the sector and start the
engine. If the engine
is cranked by hand the
spark lever should be
placed at the extreme
left on the sector.
Run the engine until
the water jacket on
the intake pipe is hot.
Move the spark
lever to the extreme
left on the sector and
the throttle lever to a
position which leaves
the throttle in the carburetor
slightly open.
Fig. 21.
Carburetor, Side View.
Adjust the air valve screw "A," Fig. 21, to a point which produces the
highest engine speed. Turning the screw "A" in a clockwise direction increases
the proportion of gasoline to air in the mixture and vice versa.
Close the throttle (move it to the extreme left on the sector) and
adjust the throttle stop screw "B" to a point which causes the engine to run
at a speed of about 300 revolutions per minute. The spark lever should be
at the extreme left on the sector when this adjustment is made.
With the spark and throttle levers at the extreme left on the sector
adjust the air valve screw "A" to a point which produces the highest engine
speed.
Open the throttle until the shutter attached to the right hand end of the
throttle shaft just covers the slot in the carburetor body. Then adjust the
screw "G" to a point which produces the highest engine speed or to a point
ADJUSTMENTS 49
where the engine slows down slightly from a lean mixture. Turning the
screw "G" in a clockwise direction increases the proportion of gasoline to
air in the mixture and vice versa.
During very cold weather when a slightly richer mixture is desirable it
may be found best to turn the adjusting screw "G" further in a clockwise
direction.
PERSONAL DANGER IN RUNNING ENGINE IN CLOSED
GARAGE.
Carbon monoxide, a deadly poisonous gas, is present in the exhaust of
gasoline engines. Increasing the proportion of gasoline to air in the mixture
fed to the engine, in other words, enriching it, increases the amount of carbon
monoxide given off at the exhaust pipe.
Because of the presence of carbon monoxide it is very dangerous to run
the engine for any length of time while the car is in a small, closed garage.
If the doors and windows are open the danger is very much lessened, but it
is far safer, particularly if an adjustment of the carburetor is being made, to
run the car into the open.
Serious personal injury may be caused by the presence of carbon monoxide
in a garage if the percentage of it in the air is greater than a very
small fraction of one per cent. Unconsciousness may result without warning.
It is reported that no indication of danger is given by personal discomfiture
until too late. Deaths resulting from the presence of carbon monoxide in
garages have been reported.
LEANING DEVICE
A leaning device, sometimes called a "gas-saver," is provided which mav
be adjusted to cause, for ordinary driving speeds, a mixture in which the proportion
of gasoline to air is. cut down. The mixture is not affected by the
leaning device at the closed or nearly closed position of the throttle, or at
the open or nearly open position.
The leaning device is adjusted at "G," Fig. 21. When the adjusting screw
"G" is screwed in as far as it will go the leaning device has no influence on
the mixture at any throttle position.
The leaning device consists of a shutter, attached to the right hand end
of the throttle shaft, which covers a slot in the carburetor body when the
throttle is opened slightly, again uncovering the slot when the throttle is
opened wide or nearly so. A hole is drilled through the carburetor body from
the mixing chamber to the slot and another hole is drilled from the carburetor
bowl to the slot.
When the slot is covered by the shutter a passage is formed from the
mixing chamber to the carburetor bowl. The partial vacuum in the mixing
chamber causes a lowering of the atmospheric pressure in the carburetor bowl
resulting in less gasoline being fed through the spray nozzle. When the
shutter uncovers the slot the partial vacuum in.the mixing chamber has no
effect on the atmospheric pressure in the carburetor bowl and the amount of
gasoline fed through the spray nozzle is not affected.
AUTOMATIC THROTTLE
The carburetor is equipped with an automatic throttle, Fig. 22, controlled
by a spring. Its purpose is to prevent pulsations of air in the intake
manifold from causing the air valve to flutter when the engine is running
slowly with the throttle fully opened. The automatic throttle is adjusted
when the carburetor is assembled and requires no further attention.