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).


Previous page  1927 Supplement Home  Next page

Carburetor Manuals: Packard