Use the information given in this section in conjunction with Section D.
Sections DDD.1 to DDD.5 should be used for carburetters fitted with the auxiliary thermo carburetter. This information supersedes that given in Sections D.12 and and D.13. Full information is given in Sections DDD.6 to DDD.9 and DDD.11 for the carburetters fitted to the Austin-Healey 3000, Mk.11.
The two S.U. H.D. carburetters are fitted with pancake type air cleaners.
A damper is provided in each carburetter, consisting of a plunger and non-return valve attached to the oil cap nut, and operates in the hollow piston rod which is partly filled with oil. Its function is to give a slightly enriched mixture on acceleration by controlling the rise of the piston, and to prevent piston flutter.
Remove the suction chamber cap and damper assembly and replenish the oil reservoir as necessary every 3,000 miles (4800 km.).
The carburetter differs from the more familiar S.U. type in so far that the jet glands are replaced by a flexible diaphragm, and the idling mixture is conducted along a passage-way, in which is located a metering screw, instead of being controlled by the throttle disc.
An auxiliary carburetter controlled by a thermo- switch, provides the enriched mixture required when starting from cold. The fuel for this carburetter is drawn from the rear main carburetter supply but its operation is completely independent.
The jet (I), Fig. DDD.2, which is fed through its lower end, is attached to a synthetic rubber diaphragm (5) by means of the jet cup (4) and jet return spring cup (7), the centre of the diaphragm being compressed between these two parts; at its outer edge it is held between the diaphragm casing (9) and the float-chamber arm. The jet (1) is controlled by the jet return spring (8) and the jet actuating lever (lo), the latter having an adjusting screw (15) which limits the upward travel of the jet (1) and thus constitutes the idling adjustment; screwing it in (clockwise) enriches the mixture, and unscrewing it weakens the mixture.
Provision is made for the use of throttle spindle glands consisting of the cork gland itself (17), a dished retaining washer (18), a spring (20) and a shroud (19). This assembly should not require servicing and can only be removed by dismantling the throttle spindle and disc.
The connection (13) to the vacuum ignition control is made at the top of the carburetter instead of underneath or at the side, as with the older type.
The H.D. carburetter still idles on the main jet, but the mixture, instead of passing under the throttle disc, is conducted along the passage-way (11) connecting the air intake passage to the manifold side of the throttle disc.
The quantity of mixture passing through the passage- way (11) and, therefore, the idling speed, of the engine, are controlled by the
slow-run valve (12) the quality or relative richness of the mixture being determined by the jet adjusting screw (15).
It follows that when idling, once the engine has reached its running temperature, the throttle remains completely closed against the bore of the carburetter.
The enrichment apparatus to assist cold starting is, in effect, an auxiliary carburetting system and is shown in Fig. DDD.3. The main body casting (36) containing a solenoid operated valve and fuel metering system is attached by means of a ducted mounting arm to the base of the main carburetter fuel inlet.
The auxiliary carburetter forms, therefore, a separate unit additional to the normal float-chamber, but drawing its fuel supply directly from it. Fuel is supplied to the base of the jet (29) which is obstructed to a greater or lesser degree by the tapered slidableneedle (25).
When the device is in action air is drawn from the atmosphere through the air intake (26) and thence through the passage (28), being carburetted with fuel as it passes the jet (29). The mixture is thence carried upwards past the shank of the needle (25) through the passage (37) and so past the aperture provided between the valve (33) and its seating (35). From here it passes directly to the induction manifold through the external feed pipe shown.
The device is brought into action by energizing the winding of the solenoid (31) from the terminal screws (30). The centrally located iron core (32) is thus raised magnetically, carrying with it the ball-jointed disc valve (33) against the load of the small conical spring (34) and thus uncovering the aperture provided by the seating (35).
Considering the function of the slidable needle (25), it will be seen that this is loaded upwards in its open position by means of the slight compression spring (24) which abuts against a disc (23), attached to the shank of the needle. The needle continues upwards through the vertically adjustable stop (22) in which it is slidably mounted and it finally terminates in an enlarged head.
Depression within the space surrounding the spring (24) is directly derived from that prevailing in the induction tract, and this exerts a downward force upon the disc (23), which is provided with an adequate clearance with its surrounding bore. This tends to overcome the load of the spring (24) and to move the needle downwards, thus increasing the obstruction afforded by the tapered section which enters the jet (29).
The purpose of this device is to provide two widely different degrees of enrichment, the one corresponding to idling or light cruising conditions and the other to conditions of open throttle or full-power operation. In effect, under the former conditions the high induction depression prevailing will cause the disc (23) to be drawn downwards, drawing the tapered needle into the jet (29), while under the latter, the lower depression existing in the induction tract will permit the collar to maintain its upward position with the needle withdrawn from the jet. The only adjustment provided is the needle stop screw (22) which limits the degree of movement provided for the needle assembly.
The size and degree of taper of the lower end of the needle (25),the diameter of the disc (23), and the load provided by the spring (24) are not adjustable.
The solenoid (31) is energized by means of a thermo- statically operated switch housed within the cylinder head water jacket. This is arranged to bring the apparatus into action at temperatures below (86-95°F.) 30-35°C.
This is carried out in much the same way as on the standard H-type carburetter, except that the float chamber and jet casing must be removed and the jet held in the uppermost position by hand. It is important to keep the diaphragm and, therefore, the jet in the same radial position in relation to the carburetter body and jet casing throughout this operation, as the jet orifice is not necessarily concentric with its outside diameter, and turning might cause decentralisation. The simplest way to do this is to mark one of the diaphragm and corresponding jet casing screw holes with a soft pencil.
The adjustment of the M.D. carburetter is extremely simple. Whereas with the older type the jet was controlled by a nut, it is now set by a screw (15), and whereas the engine speed was determined by adjustment of the throttle, it is now controlled by the
slow-run valve (12). To enrich the mixture the screw (15) should be screwed in, and to increase the idling speed the
slow run valve (12) should be screwed out.
The adjustment procedure is as follows:-
slow runningif necessary.
NOTE.-Should difficulty be experienced when starting from cold on the next occasion, unscrew the stop screw (22) one or two flats only.
Since the jet of the H.D. carburetter is fed through its centre and has no glands, leakage can only be caused by an insecure fit of the jet cup, an imperfect seal of the diaphragm, either at its outer edge, where it is com- pressed between the float-chamber and the diaphragm casing, or at its inner edge, where it is fitted to the jet, or by fracture of the diaphragm. Leakage at the outer edge may be cured by tightening the float-chamber securing screws (6) but fracture or leaking at the inner edge will probably call for a new jet assembly.
The jet may also stick, either up or down, due to dirt between it and its bearing (2), or due to corrosion, The cure is to remove the parts by undoing the jet screw (3), clean, and refit.
To remove the carburetters from the inlet manifold proceed as follows :-
If only one carburetter is to be removed the inter- connecting petrol pipe must be released. In this case it is also necessary to split the throttle shaft at the centre connecting clip.
To improve starting characteristics, the green spring (24) Fig. DDD.3, fitted to the starting jet needle has been changed to a blue spring (Part No. AUC1041) commencing at engine No. 3664. It is recommended that all engines between 2864 and 3664 be checked and that the blue spring be fitted if it is not already incorporated.
Commencing at chassis Nos. BN5234 and BT5310, standard type H.D. carburetters and hand choke controls were fitted.
The fitting of the H.D. type carburetter with the cold start device has been discontinued.
The fuel pump on the BT.7 is situated under the left hand seat pan, and is accessible when the seat pan has been removed.
The BN.7 has the fuel pump fitted on the left hand side of the car and access to it is obtained through the hinged portion of the spare wheel floor, as for the batteries (See Section NN.1).
The carburetters fitted to the Healey 3000 Mk. II are triple S.U. type H.S.4. Each carburetter is mounted on an individual manifold secured to the cylinder head by three studs and nuts, and interconnected by an external balance pipe running above the manifolds.
The H.S.4 carburetter is of the automatically expanding choke type in which the size of the main air passage (or choke) over the jet, and the effective area of the jet, are variable according to the degree of throttle opening used on the engine against the prevailing road conditions (which may differ widely from light cruising to heavy pulling).
Therefore, to serve the complete throttle range a single jet only is used, being a simple metal tube sliding in a single bearing bush, fed by fuel along a small- diameter nylon tube leading direct from the base of the float-chamber. The jet is varied in effective area by a tapered fuel metering needle.
Slow-running is governed by the setting of the jet adjusting nuts and the throttle adjusting screws, all of which must be correctly set and synchronized if satisfactory results are to be obtained.
Before blaming the carburetter setting for incorrect slow-running make certain that the trouble is not caused by badly adjusted distributor contact points, faulty plugs, incorrect valve clearance, or faulty valves and springs.
After the first 1,000 miles (1,600 km.) or so when the engine is fully run in, the slow running may require adjustment. This must only be carried out when the engine has reached its normal running temperature.
As the needle size is determined during engine development, tuning of the carburetters is confined to correct idling setting. Slacken the actuating arms on the throttle spindle inter-connection. Close all throttles fully by unscrewing the throttle adjusting screws, then
open each throttle by screwing down the idling adjustment screws one turn.
Remove pistons and suction chambers, and dis- connect the jet control cables. Screw the jet adjusting nuts until each jet is flush with the bridge of its carburetter, or as near to this as possible (all jets being in the same relative position to the bridge of their respective carburetters). Replace the pistons and suction chamber assemblies, and check that the pistons fall freely on to the bridge of the carburetters (by use of the piston lifting pins). Turn down the jet adjusting nut two complete turns (12 flats).
Re-start the engine, and adjust the throttle adjusting screws to give the desired idling speed, by moving each throttle adjusting screw an equal amount. By listening to the hiss in the intakes, adjust the throttle adjusting screws until the intensity of the hiss is similar on all intakes. This will synchronize the throttle setting.
When this is satisfactory, the mixture should be adjusted by screwing each jet adjusting nut up or down by the same amount, until the fastest idling speed is obtained consistent with even firing. During this adjusting, it is necessary that the jets are pressed upwards to ensure that they are in contact with the adjusting nuts.
As the mixture is adjusted the engine will probably run faster, and it may therefore be necessary to unscrew the throttle adjusting screws a little, each by the same amount, to reduce the speed.
Now check the mixture strength by lifting the piston of the front carburetter by approximately 1.32in. (.75mm.) when if:
the engine speed increases, this indicates that the mixture strength of the front carburetter is too rich.
the engine speed immediately decreases, this indicates that the mixture strength of the front carburetter is too weak.
the engine speed momentarily increases very slightly, then the mixture strength of the front carburetter is correct.
Repeat the operation at the centre and rear carburetters, and after adjustment re-check the front carburetter, since all carburetters are inter-dependent.
When the mixture is correct the exhaust note should be regular and even. If it is irregular with a splashy type of misfire and colourless exhaust, the mixture is too weak. If there is a regular or rhythmical type of misfire in the exhaust beat, together with a blackish exhaust, then the mixture is too rich.
The carburetter throttle on each carburetter is operated by a lever and pin, with the pin working in a forked lever attached to the throttle spindle. A clearance exists between the pin and the fork, which must be maintained when the throttle is closed and the engine idling, to prevent any load from the accelerator linkage being transferred to the throttle butterfly and spindle.
To set this clearance: with the throttle shaft levers free on the throttle shaft, put a .12 in. (.305mm.) feeler between each throttle shaft stop at the top and the carburetter heat shield (see Fig. DDD.5). Move each throttle shaft lever downwards in turn until the lever pin rests lightly
on the lower arm of the fork in the carburetter throttle lever. Tighten the clamp bolt of the throttle shaft lever at this position. When all three carburetters have been dealt with, remove the feelers, The pins on the throttle shafts should then have clearance in the forks.
Re-connect the choke cables, ensuring that the jet heads return against the lower face of the jet adjusting nuts when the choke control is pushed fully in.
Pull out the mixture control knob on the dash panel to its maximum movement without moving the carburetter jets (about +in.) (15.87mm.) and adjust the fast idle cam screws to give an engine speed of about 1,000 r.p.m. when hot.
The position of the forked lever in the float-chamber must be such that the level of the float (and therefore the height of the fuel at the jet) is correct.
This is checked by inserting a -&-in.(7.94mm.) round bar between the forked lever and the machined lip of the float-chamber lid. The prongs of the lever should rest on the bar (see Fig, DDD.6) when the needle is on its seating. If this is not so, the lever should be reset at the point where the prongs meet the shank, Care must be taken not to bend the shank, which must be perfectly flat and at sight angles to the needle when it is on its seating.
To check the jet for concentricity with the jet needle, set the jet head and the jet adjusting nut in the upper- most position, lift the suction piston with the piston lifting pin and allow the piston to fall. It should fall freely and a definite soft metallic click will be heard as the base of the piston strikes the jet bridge.
If this does not happen with the jet raised, but does occur when the jet is lowered, the jet bearing and jet must be recentred as follows:-
Disconnect the link between the jet head and carburetter lever by removing the small Phillips retaining screw from the jet head.
Unscrew the union securing the jet feed tube into the base of the float chamber and withdraw the jet from the jet bearing, complete with feed tube.
Unscrew the jet adjusting nut and remove the lock spring; screw up the nut to its fullest extent and refit the jet head and feed tube. Slacken the jet locking nut until the jet bearing is just free to rotate with finger pressure. Remove the piston damper from the top of the suction chamber body and gently press down the piston on to its stop.
Tighten the jet locking nut, at the same time ensuring that the jet head is held firmly in its uppermost position and at its correct angular relation to the float chamber.
Repeat the check for concentricity both with the jet raised and lowered. If the result is not satisfactory the recentering operation must be repeated until the correct result is obtained.
When the operation is completed, replace the adjusting nut lock spring and the jet operating link.
This adjustment is best effected with the carburetters removed from the engine.
If the engine runs unevenly, apparently through lack of fuel, when there is plenty in the tank and the pump is working properly, the probable cause is a sticking float needle. An easy test for this is to disconnect the pipe from the electric pump to the carburetter and switch the ignition on and off quickly while the end of the pipe is directed onto a pad of cloth or into a container.
If fuel is delivered, starvation is almost certainly being caused by the float needle sticking to its seating, and the float chamber lid(s) should therefore be removed and the needle and seating cleaned and refitted.
At the same time it will be advisable to clean out the entire fuel feed system as this trouble is caused by foreign matter in the fuel, and unless this is removed it is likely to recur. It is of no use whatever renewing any of the component parts of the carburetter(s), and the only cure is to make sure that the fuel tank and pipe lines are entirely free from any kind of foreign matter or sticky substance capable of causing this trouble.
The piston assembly comprises the suction disc and the piston forming the choke, into which is inserted the hardened and ground piston rod which engages in a bearing in the centre of the suction chamber and in which is, in turn, inserted the jet needle. The piston rod running in the bearing is the only part which is in actual contact with any other part, the suction disc, piston, and needle all having suitable clearances to prevent sticking. If sticking does occur the whole assembly should be cleaned carefully and the piston rod lubricated with a spot of thin oil, No oil must be applied to any other part except the piston rod. A sticking piston can be ascertained by removing the piston damper and lifting the piston by pressing the piston lifting pin; the piston should come up quite freely and fall back smartly onto its seating when released. On no account should the piston return spring be stretched or its tension altered in an attempt to improve its rate of return.
The fuel pipe connecting the front and centre carburetters, and the air cleaners, are removed for clarity.
Should this be suspected, lift the piston with a pencil when the jet can then be seen. Flood the carburetter and watch the jet; if fuel does not flow freely there is a blockage. To remedy this start the engine, open the throttle, and block up the air inlet momentarily, keeping the throttle open until the engine starts to race.
If the jet is completely blocked and the engine will not run correctly, the jet must be removed and thoroughly cleaned.
This is indicated by fuel flowing from the drain hole in the top of the float chamber lid below the main fuel feed pipe, and is generally caused by grit between the float chamber needle and its guide. The float-chamber lid should be removed and the needle and its guide thoroughly cleaned.
Turn the battery master switch to the
Disconnect the fuel feed pipe from the front carburetter, the two snap-lock ball joints from the accelerator relay shaft, and the three throttle return springs.
Release the three mixture control cables from the carburetter levers. Slacken the retaining clip and remove the engine breather hose from the rear air cleaner. Pull off the rubber connector for the vacuum ignition control pipe from the top of the rear carburetter body.
Remove the two nuts, spring washers and plain washers securing each carburetter flange and withdraw the three carburetters as one unit.
Detach the throttle interconnecting shafts, remove the fuel pipes and separate the carburetters.
Refitting is a reversal of the removing procedure.
The throttle linkage must be checked and readjusted if necessary after refitting.
Flexible plastic overflow pipes were fitted to each carburetter float chamber from Power Unit No. 29E-H-1092. The float chamber lids were modified to incorporate short overflow nozzles on to which the flexible pipes are a push fit. The overflow pipes may be fitted with the modified lids to earlier 3000 Mk. II cars.
Carburetters fitted to later 3000 Mk. II cars incorporated float chambers equipped with nylon floats in place of the metal floats used previously. The nylon floats are integral with the float levers which are attached to the float chamber lids. The nylon float and lever assembly may be interchanged with the earlier metal float and separate lever. Red aluminium tags were used for a time to identify carburetters modified in this way.
To check the float level, hold the float chamber lid and float assembly upside down and place a -& in, (3.18 mm.) diameter bar across the diameter of the machined lip of the float chamber lid, parallel with the float lever hinge pin, and under the float lever (see Fig. DDD.9). The face of the float lever should just rest on the bar when the needle valve is fully on its seating. If it does not do this, carefully reset the angle made between the straight portion of the float lever and its hinge until the correct position is obtained.
From Car No. 17547 (BN7) and 17352 (BT7) the fuel pump and fuel lines were transferred from the left- hand side to the right-hand side of the car. The re- positioning of these components isolates them from the exhaust system and diminishes any possibility of fuel vaporization. This change involved the introduction of new fuel pipes between the tank and the pump, and between the pump and the flexible pipe leading to the carburetters, new petrol pipe fittings, and associated body modifications.
On the BT7 the fuel pump is now accessible when the right-hand rear seat pan has been removed.
Access to the fuel pump on the BN7 is obtained in the same way as before (see Section DDD.5) although it is now located on the right-hand side.
A. 1/2 in. diameter bar. B. Machined lip. C. Float lever resetting point. D. Needle valve assembly. E. Hinge pin.
The Austin-Healey 3000 Mk. XI Sports Convertible (Series BJ7) is equipped with twin S.U. carburetters, type HS6. Each carburetter is attached by four studs and nuts to a detachable one-piece six port induction manifold (see Section A.36). The carburetter float chambers incorporate nylon floats (see Section DDD.1O) and are fitted with flexible overflow pipes (see Section DDD.9).
The construction and servicing of the HS6 carburetter are basically similar to that of the HS4 type described in Section DDD.6 For the description and servicing procedure applicable to the carburetters fitted to Convertible models, refer to Section DDD.6, but note the following differences.
The instructions given under
Slow running adjustment and synchronisation in Section DDD.6 for the slow running and mixture adjustment of the triple carburetter layout apply also to the twin HS6 carburetters. When setting the throttle linkage, however, use the method given below.
The throttle on each carburetter is operated by a lever and pin, with the pin working in a forked lever attached to the throttle spindle. A clearance exists between the pin and fork which must be maintained when the throttle is closed and the engine idling, to prevent any load from the accelerator linkage being transferred to the throttle butterfly and spindle.
To set this clearance, with the throttle shaft levers free on the throttle shaft, put a ,012 in. (-305 mm.) feeler between the throttle shaft stop and its abutment on the inlet manifold (see Fig. DDD.10). Move each throttle shaft lever downwards in turn until the lever pin rests lightly on the lower arm of the fork in the carburetter throttle lever. Tighten the clamp bolt of the throttle shaft lever at this position. When both carburetters have been dealt with, remove the feeler. The pins on the throttle shaft levers should then have clearance in the forks.
Re-connect the choke cables, ensuring that the jet heads return against the lower face of the jet adjusting nuts when the choke control is pushed right in.
Pull out the mixture control knob on the fascia panel to its maximum movement without moving carburetter jets, i.e. about 5/8in. (16 mm.). With the control in this position, adjust the fast idle cam screws to give an engine speed of approximately 1,000 r.p.m. when hot.
Refer to Section DDD.10 for the method of checking and adjusting the level of the nylon floats.
Turn the battery master switch to the
Disconnect the fuel feed pipe from the front carburetter, the snap-lock ball joint front tile accelerator relay shaft, and the two throttle return springs.
Release the two mixture control cables from the carburetter levers. Remove the engine breather hose from the rear air cleaner. Pull off the rubber connector for the ignition vacuum control pipe from the top of the rear carburetter body.
Remove the four nuts, spring washers and plain washers securing each carburetter flange and withdraw the two carburetters as a unit complete with the Boat chamber overflow pipes.
Detach the throttle interconnecting shaft, remove the fuel bridge pipe, and separate the carburetters.
Reverse the above procedure when replacing the carburetters and, in addition, check the throttle linkage and re-adjust if necessary.