CARBURETORS: PACKARD
By pulling the carburetor control all the way out, the auxiliary
air intake is completely closed and the primary intake practically
closed, allowing a very rich mixture to be draw n into the cylinders.
The control should he pushed in, at least part way, as soon as
the engine has started firing.
The throttle valve (5) is of the butterfly type and is located
in the carburetor body above the spray nozzle (26). It is controlled
by a hand lever on the steering wheel and by the accelerator pedal.
An adjustable stop screw (7) holds the throttle valve (5) slightly
open and allows a small amount of mixture to reach the cylinders
with the throttle lever above the steering wheel in the closed
position. The minimum amount of mixture for idling is thus supplied.
To increase the minimum speed, loosen the cheek nut (R) and turn
the set screw (7) to the right. To decrease the speed, back off
the set screw.
The auxiliary air valve (32) is in a housing forward of the mixing
chamber and is controlled by the tension of two springs (39, 41),
one within the other.
At low speed most of the air is admitted through the primary air
intake around the spray nozzle (26).
To prevent too rich a mixture at greater throttle openings, the
auxiliary air valve (32) is opened be-cause of the increase in
suction. The carburetor thus automatically produces a more nearly
correct mixture for all engine speeds than could be obtained by
manual control.
The normal running position for the carburetor auxiliary air valve
is attained when the carburetor control is against the instrument
board. The engine while cold, however, will require a richer mixture
initially than after it has become warm by running. This rich mixture
may he obtained by keeping the control two or three notches out.
Due to the thermostatic water control, the engine warms up very
rapidly and the control should not he allowed to remain out of
normal running position any longer than is necessary.
If convenient, idle a cold engine after it has been started before
running the car. By allowing the engine to heat up in this way,
it will pull with greater efficiency when put under load.,
Too rich a mixture supplied to an engine will cause a waste of
gasoline, an accumulation of carbon, may seriously interfere with
the proper lubrication of the cylinder walls, and is apt to foul
spark plugs.
Caution: When supplied with too rich a mixture, either through
choking the carburetor too much in starting or through operating
the engine with the carburetor control too far out, the engine
is liable to refuse to run.
To overcome the "loading," open throttle and crank the
engine by the starter and with the carburetor control pushed against
the dash. After the cylinders are blown out, partially close throttle
and start the engine in usual way.
Auxiliary air valve adjustment: Permanent adjustment of the auxiliary
air valve (32) is made by changing the tension of air valve springs
(39 and 41).
'A i," (.031") gap at spark plugs gives a good spark
for slow running and for hard pulling and is the best all around
adjustment obtainable.
"- The location of this suction tube, as applied to the carburetor
with fuelizer, can be seen by referring to Fig. 52, page 140.
These springs which control the action of the valve are, in addition,
adjusted for temporarily varying operating conditions by means
of a cam on camshaft (35) which is operated by the carburetor control
on the instrument board.
The proper adjustment, for normal running conditions is obtained
when the carburetor control is against the instrument hoard. To
enrich the mixture, pull the control out as required.
The auxiliary air valve (32) itself should be adjusted to the
leanest possible mixture at which the engine will idle properly
when hot.
The dash adjustment should be pushed all the way in and the air
valve (32) should have a drop from its seat when depressed to the
point where air valve spring nut (42) touches inside spring (41).
To check, proceed as follows: Push the carburetor control all
the way in. Measure height of top of air valve stem (40) from some
fixed point on the engine. Depress air valve until nut (42) strikes
inside spring (41). Measure height of top of stem as before. The
difference in these two measurements is the air valve drop.
The outer spring (39) should be adjusted so that the air valve
just touches its seat when the carburetor control is against the
dash. Then with the engine warm reduce compression of this spring
as much as possible, retaining smooth engine operation.
Make sure that air adjusting connecting rod clevis is so adjusted
that the air shutter (29) completely closes when the carburetor
control on the instrument board is pulled all the way out.
Caution: In warm weather, or if the engine is warm, the mixture
may be so rich if the carburetor control is pulled out too far
that the charge will not ignite and the surplus of unburned gasoline
may interfere with the proper lubrication of the cylinder walls.
See Caution in left column.
Suction tube: A suction tube= leads from the base of the spray
mixing tube (26) into the upper part of the mixing chamber above
the throttle valve.
The function of this tube is to prevent loading of the engine when
it is idled or driven by the car in coasting with the clutch engaged.
This is accomplished by the tube removing the gasoline which collects
in carburetor body due to condensation.
It also prevents loading under continued low throttle driving and
aids in giving immediate response in acceleration.
Failure of the suction tube to function properly is evidenced usually
by gasoline dripping from the carburetor and by loading of the
engine as described.
The cause of failure would be air leakage into the tube or connections,
or, more frequently, clogging of the passage way either in the
tube elbow or carburetor body.
The best way to clean this passage way is to re-move the tube
and blow it out, together with the lower elbow connection and the
drilled leads in the carburetor, with compressed air.
Float-level adjustment: The needle valve (16) (Fig. 1) must have
not less than 5" movement. Solder collar (13) and needle valve
after adjusting. With gasoline level %" below top of tube
(26), float weights (14) must be approximately horizontal (position
as shown in Fig. 1).
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