CARBURETTOR (" 75" models)

(SOLEX TYPE 30 PAAI2 with progressive starter and combined two-phase acceleration and economy device).

IT MUST BE EMPHASIZED THAT ON LEAVING THE WORKS THE JET-SETTINGS, etc., ARE FIXED AT VALUES SHOWN BY EXPERIENCE TO BE MOST SUITABLE FOR THE ROVER CAR.

The descriptive details which follow will be more clearly understood by constant reference to the cross-sectional' view of the carburettor in Fig. 22.

THE PROGRESSIVE STARTER.
This unit is a small auxiliary carburettor which provides a suitably enriched mixture of air-petrol for starting from cold and warming up the engine until approximately normal running temperature is reached.

It has two jets, the sizes of which can be varied, viz.: the air jet (Ga) and the petrol jet (Gs). The selection of the appropriate sizes of each, dependent on cylinder capacity, controls the mixture strength for cold starting.

This device operates as follows -When the engine is rotated the depression created in the
induction manifold is communicated to the well located above the petrol jet (Gs). The petrol is lifted to the top of the well, passes down the channel (b) and through the orifices (01) and (02) already uncovered by the movement to the left of the piston (C), operated from the driver's seat by means of the "Cold Start" control.

As the engine warms up, its speed increases, and in consequence, so does the quantity of air drawn through the air jet (Ga). The petrol supply, however, increases much less rapidly, for once the contents of the well above, the petrol jet (Gs) are exhausted, the rapidity of its replenishment is controlled by the size of the jet (Gs), and is further retarded by air drawn down the channel (e), thus relieving the depression or suction on the jet (Gs).

Finally, further progressive weakening occurs until the supply from 'the starter unit is completely cut off as the control is released, the result of which is that the spring-loaded piston (C) moves to the right, successively sealing the holes (01) and (02).

TO START THE ENGINE FROM COLD.

Pull out fully the " Cold Start " control, and press the starter button without touching the accelerator, i.e., the throttle butterfly must remain in the idling position. The engine will start immediately and, as soon as its speed begins to rise, the dashboard control may be gradually released. When the engine has warmed up to running temperature as indicated by the appearance of the amber warning light, release the control altogether, when the Solex Starter will be completely out of action.

By adhering to these directions the greatest advantage is obtained from the Progressive Starter, i.e., an amply rich mixture for immediate cold starting even at extraordinarily low temperatures, and semi-automatic weakening off as the engine speed and temperature rise.

FUNCTION.

THE ACCELERATION DEVICE.
This consists of a box-like structure situated at the side of the carburettor and exteriorly fitted with a jet (Gu).

The internal components comprise the following -

(i) A pump shaft ultimately actuating a ball valve (H), in front of which is a light spring. The shaft passes through and is affixed to the centre of a flexible membrane (Mm).

(ii) To the right of the membrane (Mm) is a chamber containing a compression spring (r). This chamber is subject to induction depression via the channel (d) having its exit at a point in the throttle chamber on the engine side of the throttle (v).

(iii) Further still to the right is another chamber, one wall of which consists of a flexible membrane (M) spring loaded, and. centrally from which protrudes a short rod in clearance contact with fulcrumed lever (1). The lever (1) slides on to a spring loaded horizontal rod, the effective length of which is determined by the adjustment of the nut (e). The rod is fixed at its end to a small lever fitted to one end of the carburettor spindle.

The chamber through which the pump shaft passes to the left of membrane (Mm) is in communication with the chamber containing the compression spring to the left of the membrane (M). Both chambers are filled with petrol via the ball valve (ci) prior to the functioning of the device and the contents of both are equally affected thereby.

FUNCTION AND ECONOMY ACTION.
When the butterfly (v) is nearly closed and the vehicle travelling at very low speed, the central chamber containing the spring (r) is subject to high induction depression. The membrane (Mm) to which the pump shaft is affixed, subject to the same depression, flexes to the right compressing the spring (r) and the ball valve (H) is on its seating, being held firmly there by pressure of the light spring to the left of it.
t this stage the spring loaded lever (l) is lightly-in contact with the end of the rod affixed to the centre of the membrane (M).

On opening the throttle to accelerate, the immediate sequence of events is as follows -The lever (l) forces the rod, and consequently the membrane (M) to the left, compressing the spring on the inner side and discharging the petrol contained in its chamber, through to the chamber on the left of the membrane (Mm), so displacing the petrol contained therein. This displacement forces the ball valve (H) off its seating, and the petrol is discharged via the calibrating units (Ca) from the injector tubes (i) into the central air streams passing down the choke tubes (K).

Thereafter, the induction depression rapidly falls in the central chamber as the throttle opens, and the spring (r) expands, flexing the membrane (Mm) to the left thereby discharging the residue of petrol contained in the chamber to the left of it, to emerge via the injector tubes (i) as just described.
Now let us consider the function of the jet (Gu) often referred to as the "economy jet" since such is its effect in the final stages of carburation.

Consider first of all what takes place at high speeds with the throttle fully or almost fully open.
The depression in the induction manifold is low and consequently negligible in the central chamber containing the spring (r). Thus the ball valve (H) is pushed off its seating and petrol is free to flow via the valve (ci) through the chamber on the left of the membrane (Mm) and so past the ball valve (H) to the injector tubes (i}. This flow is obviously supplementary to the output of the main jets (Gg).
The calibrations (ca) of the injector tubes have been determined to ensure the best acceleration and the main jets of such a size that their output, supplemented by the output of the injector tubes are together equal to the requirements of the engine at major throttle openings.

At lower throttle openings, however, when the depression in the central chamber is high and the ball valve (H) in consequence seated, the main jets may be too small for optimum carburetion efficiency and supplementary petrol is therefore needed to maintain the correct standard of output.
Thus the economy jet (Gu) is installed and it will be obvious that with the pump valve closed, petrol is free to flow from the carburettor float chamber via the economy jet (Gu) and so to the injector tubes (i). On the size of (Gu) therefore depends the fuel flow needed by the engine for good performance and maximum economy in the circumstances described, viz., at "cruising" speeds.

GENERAL NOTES

STARTING THE ENGINE WHEN COLD.

Pull out fully the "Cold Start" control.
Switch on the ignition and press the starter button, without depressing the accelerator pedal, and the engine will start.

When the engine is running, release the control gradually, your objective being to dispense with it altogether when the engine reaches normal working temperature as indicated by the appearance of the amber warning light.

When the engine is hot, particularly in summer, it should not be necessary to make use of the Solex Starting device. The engine will start easily on the pilot jet output, if it and the carburettor are in good mechanical condition; if difficulty is experienced, depress the accelerator until the engine fires.

TO SET THE IDLING.

It is important to ensure that the idling mixture via both throttles is correctly balanced. The following method is recommended.

Run the engine until well warmed. Then stop it and screw home fully (not using excessive force) both volume control screws (W). Then unscrew them one full turn. Start the engine. Check the idling speed of the engine, adjusting the speed by means of the throttle stop screw fitted to the throttle lever abutment plate.
If in the attempt to obtain satisfactory idling in this way, the engine "hunts," screw in both volume control screws carefully each the same amount.

If, on the other hand, the engine fires erratically, the mixture is too weak and the volume control screws must be slackened still more.

The engine is very sensitive to these adjustments and great care is necessary to adjust the volume control screws in unison.

If by these means it is found impossible to obtain good idling, examine the carburettor carefully, checking the points of the volume control screws to see that they have not been distorted or broken and are clean. All the carburettor assembly screws must be tight and, of course, the flange washer intact and forming an airtight seal.

If all is well, bad idling can then be due only to some engine or ignition defect, and it is well to bear in mind that the timing of the ignition, condition of the plugs and valve timing all have a considerable effect upon the idling.
The metering of the pump output is determined by the careful selection of the calibrated injector units or jets (Ca) and the economy jet (Gu} and it is emphasised that no alteration should be made to these without first consulting us.

If, after prolonged use, it appears that the accelerating device is not working satisfactorily, make sure that there is no dirt lodged, in the calibrating units (Ca) or higher up in the injectors (i) themselves.

If the pump appears to be defective, do not try to overhaul or repair it. Your Rover agent will be able to help you and fit a new pump assembly if required.

We would emphasise, however, that the actual pump deterioration- is extremely unlikely to occur, and that if it does, the general condition of the carburettor is such that a general overhaul or complete replacement is desirable.

RECOMMENDATIONS FOR CARBURETTOR FITMENT.
Use the flange washer provided or one no thicker. A thick flange washer invites distortion of the carburettor flange. See that the petrol pipe is well clear of the engine.

Tighten the flange nuts, a little at a time as you would those of a cylinder head, using for preference, split securing washers. This will safeguard against flange distortion when effecting fitment.

Take care in linking up throttle controls and throttle return springs. If the pull or push of either is not in the correct plane, rapid wear of the throttle spindle will result.

See that aft actuating joints work freely. Check that the throttle butterflies open and close fully.
When fitting the dashboard cable to the starter unit lever, avoid sharp bends, and before clamping the wire to the lever, see that the dashboard knob is about 5 mm. out from the fully home position, when the starter lever is in the "off" position.

DECARBONISING

It is not possible to lay down any hard and fast rule concerning the mileage intervals at which the engine should be decarbonised and the valves ground in, for it is not actually necessary to carry out the operation until there is a "fall-off" in performance. As that condition is not always readily detected under varying conditions of service your nearest Rover dealer will always be pleased to advise you on the matter.' If you are in any doubt at all, it is far better to depend upon mileage as your guide and decarbonise and grind in the valves every 10,000 miles (15.000 Km.).