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.

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.
 

CARBURETTER INTAKE SILENCER.
(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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