1928 Cadillac - GM Heritage Center

12 CADILLAC OPERATOR'S MANUAL
OPERATION 13
position to which it is moved, whereas the accelerator must be held down
to keep the throttle open.
The normal position of the hand lever for driving the car is all the way
up (at "Close"). In this position the throttle of the carburetor is open
just enough to permit the engine to run at idling speed after it is warm.
For starting, however, the lever should be moved approximately one-fourth
the way down, and should be left in this position until the engine is warm
enough to permit the lever to be returned to the idling position without
stalling the engine. (Also see Chapter on "Cold Weather Operation.")
Ignition Control
Correct timing of the ignition in relation to the positions of the pistons
is controlled automatically by the timer-distributor which provides for all
ordinary advancing and retarding of the spark.
A hand control is also provided, however, for further retarding of the
spark as occasion requires. The hand control is the right hand of the two
levers on the instrument board directly in front of the steering column.
When the pointer is all the way to the left the spark is fully advanced.
When the pointer is all the way to the right, the spark is fully retarded.
The correct position of the hand control lever depends on the fuel used.
Cadillac cars are equipped with what are known as high compression
cylinder heads. These are cylinder heads in which the space into which
the fuel mixture is compressed just before it is ignited is so proportioned
that a higher pressure is obtained than with low-compression cylinder heads.
High-compression cylinder heads enable the engine to develop more
power when used with anti-knock fuel. The ignition is so timed at the
factory that when the hand control lever is fully advanced the engine will
develop the maximum power possible with anti-knock fuel.
The high-compression cylinder heads do not prevent the use of regular
fuel, but when regular fuel is used the spark must be retarded slightly to
secure maximum power and prevent detonation or spark knock. The spark
should then be retarded just to the point where the engine "pings" slightly
on rapid acceleration. This slight amount of spark knock is absolutely
harmless to the engine and is an indication to the driver that the spark is
set at the point that will give maximum power and economy.
When once set, the spark control does not need to be changed unless the
fuel is changed or unless the accumulation of carbon makes it necessary.
Carbon deposit, which accumulates with use in all engines, also causes
spark knock and in time may require setting back the spark. Regardless of
the kind of fuel used or the presence of carbon, the correct setting of the
spark control at any time is at the point where the engine "pings" slightly
on rapid acceleration.
CAUTION—If the engine is being cranked bv hand the spark should
always be fully retarded.
Carburetor Enriching Control
The button at the left of the instrument panel (Fig. 5, controls a device
on the carburetor for temporarilv enriching the fuel mixture supplied to
the engine. When starting the engine, it is
necessary to have the proportion of liquid
gasoline in the fuel mixture greater than
at other times, because in a cold mixture only
a part of the gasoline is vaporized. Pulling
out the enriching button increases the proportion
of liquid gasoline to air, the normal
proportions being restored when the button
is released and permitted to return to its
original position.
Fkun 5. The carburetor enrich- r r u • I • i
ing control does not prime the car- Correct use of the enriching control not
buretor. To have any effect, it onlv is essential to quick starting of the
must be held out while the starter . , , • ^ cr ^
is cranking the engine.
engine, but also has an important effect on
the life of the engine. The enriching button
must be pulled out far enough in starting to
provide an explosive mixture quickly so that the battery is not unnecessarily
discharged by useless cranking. The button must also be
held out far enough during the warming-up period so that the engine
will run without missing and "popping back."
On the other hand, it should not be pulled out any further or held out
any longer than is necessary to accomplish these results, because some of
the excess liquid gasoline in the enriched mixture does not burn and washes
off the oil on the cylinder walls, interfering with proper lubrication of the
pistons.
If the engine still retains heat from previous running, the enriching control
should not be used without first attempting to start the engine on the
normal mixture. If the enriching button is pulled out for starting a hot
engine, the mixture may be made so rich that starting will be impossible.
The enriching button is not a priming device. It has no effect whatever
on the fuel or the fuel mixture unless the engine is being cranked or is running
under its own power. To have any effect, the button must be pulled
out and held partly out during the cranking operation.