Article Index
Austin Ten-Four Handbook (1935 Litchfield)
The New Car
Periodical Attentions
The Fuel System
The Carburetter
The Sports Model
The Ignition System
The Cooling System

Brief Working Description.

FROM the tank the petrol passes via the pump through the Union (A), the filter and the needle seating into the float chamber. The petrol rises and when reaching a certain predetermined height will cause the float to push the needle on to its seating, thus regulating the petrol flow.


A—Union. E—Stop screw. H—Petrol connector.
D—Holding-down screws. F—Air regulating screw. 1—Washers.

The float chamber contains the main jet (1), (see illustration on page 17,) compensating jet (2), compensating well (3), and slow running jet (4).

From the jets the petrol flows along two separate channels into a common channel in the emulsion block (5), which is attached to the float chamber.

The petrol in the compensating well is in direct communication with the air and with the emulsion block. Consequently, all the petrol from the jets and well is now centred in one channel in the emulsion block. This channel leads to a nozzle (6), which projects directly into the choke tube.

Procedure when Starting.

First pull out the knob fully, thus operating the air strangler, and turn the engine over a few times with the ignition switched off, which has the effect both of freeing the pistons, etc., and priming the cylinders. Then release the knob to the first notch, (B) see page 9. On switching on and again turning the engine over, it should start readily and continue to run.

It is quite In order to run for a short while with the knob in notch B. which is the " warming up " position. Then as the engine warms up, release to the second notch A, or fast idling position, until, after a few minutes the engine has reached a reasonable temperature, when the knob can be pushed right in.

Difficulty can be caused by the strangler flap not closing properly, and the control wire should be examined, and if necessary shortened, to permit the flap closing fully. A choked slow running jet will also cause the difficulty, and this part should be. taken out of the carburetter, and carefully cleaned.

Trouble can also be caused if the throttle is not opening sufficiently when the strangler knob on the dash is in the first notch B, and in this case turning the screw on the throttle lever of the carburetter a little to the right will have the effect of opening the throttle a little wider, but if this is overdone, it will affect the slow running.

If the mixture for slow running is weak, this can also cause difficulty in starting up, and in this case turn the regulating screw (F) in a clockwise direction, which will enrich the mixture for starting and slow running, but do not overdo this, as if the mixture is too rich, the engine will hunt and tend to choke when slow running with the engine warm.


The carburetter is delivered with the setting that has been found by extensive experimental work to be most suitable. Consequently, very little adjustment to the carburetter is needed. Indeed the user will find that a greater service will be obtained from the carburetter if the various screws, etc., are only moved when absolutely necessary.

On those occasions, however, when an adjustment is advisable (after a new car has been ' run in ' an adjustment of the slow running is sometimes necessary) or when the carburetter requires cleaning, the following procedure should be observed.

Slow Running.

Slow running is adjusted by means of the stop screw (E) and the air regulating screw (F).


Speed of Tick-over.

The stop screw (E) determines the speed of the slow running, I.e.. it adjusts the opening position of the throttle. To increase the slow running speed the stop screw must be turned in a clockwise direction. A turn in the opposite direction will give a slower tick over.

Richness of Slow Running Mixture.

The richness of the slow running mixture is adjusted by the air regulating screw (F). Should the engine refuse to tick over for any length of time, or stall on deceleration it is a sign that the slow running mixture is weak. To overcome this the mixture should be made richer by turning the regulating screw in a clockwise direction. If the engine is inclined to " hunt " when running slowly the mixture is too rich and must be weakened by turning the air regulating screw (F) in an anci-clockwise direction.

Poor Acceleration.

In the winter time this can very often be due to the engine not getting sufficiently hot.

If, in spite of the engine being thoroughly hot, the acceleration is bad then see to the following points.

Slow running adjustment is too weak—Try the screw (F) in a richer position.

The compensating jet "2" is too small—Try one size larger.

Lack of Power and Speed.

If this is due to the carburetter it is probably owing to the main jet being partially choked or a little too small, and the size larger should be tried. Care should be taken to make sure the lack of speed is not due to the ignition being retarded or to an insufficient supply of petrol from the tank, faulty ignition, or to poor compression due to leaking valves or wrong tappet adjustment.

Make sure also, that the strangler valve opens fully as if this sticks in a partially closed position it will restrict the speed of the car and increase consumption.

Dismantling the Carburetter

The bowl of the carburetter can be removed by taking out the holding down screws (D). A hand should be placed underneath the bowl during this operation for when the screws are removed the bowl will drop into the hand, and any petrol that is contained in the bowl can then be emptied back into the tank. On turning the bowl upside down the float will slide out and reveal the main and compensating jets at the bottom of the bowl (see illustration).

The Jets.

The jets should be removed occasionally and be thoroughly cleaned. The holding down screws (D) are milled at the end to fit into the jets. When the bottom end is placed into the jets a spanner applied to the head of the screw will enable the jets to be removed.

When cleaning the jets it is not advisable to pass anything through them that is liable to damage them. The most satisfactory and effective method is to blow through the jets and wash them in petrol. This will remove any obstruction and leave the jets undamaged.

The sizes of all jets in i-he Zenith carburetter run in fives and . the larger the number the larger the jet.

The Filter.
The petrol is filtered on entering the carburetter and the filter should be cleaned from time to time. To remove the filter unscrew the petrol connection H and pull the filter out of Its chamber. The filter gauze can then be thoroughly cleaned with petrol. When reassembling the filter care must be taken to see that the washers (J) are correctly replaced.

Alteration of the Standard Adjustment.
It is not wise to alter the standard adjustment. If the car suddenly starts to go badly, this cannot be caused by faulty carburation providing all the passages and jets are clear and there is a good supply of petrol from the main tank. Booklet giving more detailed information about the carburetter can be obtained from the Zenith Carburetter Co., 40-42, Newman Street, London, W.1.

" Leaded " Fuels
Provided that the same reasonable attention is given to valves and adjustments as with ordinary-petrols there will be no trouble when using these fuels. The appearance of the valves when running on "leaded"
fuel, differs from that associated with ordinary petrol, but this is a well recognized fact to which no significance should be attached. The deposit from such fuels can be removed by "scrubbing" the valves and their seats with a stiff wire brush, of the type used for cleaning files (a file card), after which the valves can then be "ground in" in the normal manner. We would recommend this method of cleaning for all valves whether they have operated with " leaded " or ordinary fules as it elinmates the possibility of leaving small amounts of deposit on the valve seats which tend to cause damage, or prolong the "grinding in" process.

(Export Models.)
Cleaning and Re-Oiling.
At frequent intervals, say weekly in countries where dust is constantly experienced, the A.C. oil wetted air cleaner needs cleaning and re-oiling. It is pulled off from the carburetter and the louvred end of the cleaner is swilled in a shallow pan of petrol. After drying, the metal gauze mesh should be re-oiled with
engine oil, allowing the surplus to drain off before re-fitting the cleaner. If the air cleaner is neglected it becomes choked with dirt, Sufficient air cannot pass, the mixture is too rich, and petrol consumption is increased.


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