78305 strombergCDSB 3

Starting from Cold

Carburetter type* 125 CO. 150 CD, 175 CD and 175 CD-I.

When the chokc control on the instrument panel iS pulled out it operates tnc lcv*r 6 at the side of the carburetter; this rotates the starter bar 20 to lift tho a>r valve 13 in which ii fitted the metering needle 25 from the jet orifice 19 to incrcase Uie area of the annulus between needle and orifice. In this rranner the onrlched mixture necessar/ to ensure cold starting is prowded. Simultancously, the cam on the ierucr 6 will opsn the throttle beyond the normal idlc position a«ording to tlse setting of the fast-idle stop screw 4 to -provide the fast-idle speed when the motor is cold.

When the motor fires the inereasod depression will lift the a>r valve 18 to weaken the initial starting mixture and prevent the engine stalling through ovcr richncss.

Wnlle the Choke remuns in action the car may be drivenaway but the control knob should be reicascd cr pushed in gradually as the engine attains normil working temperaturo.

It will be appreciatod thit movcment of the choke levcr 6 will dccrease progressiwsly the extent of cnrichment and degree of throttle opening for fast-idle to the point where the screw 4 is out of contact with the cam on the choke lever and the throttle is permitted to return to the normal idlc position as determincd by the setting of the throttle stop screw 3.

Carburetter types 125 CDS, 150 CDS and 175 CD-2S.

When the chokc control on the instrument panel is puiled out. it operates a lever at the aide of the carburetter; this rotates a disc in tho Starting device in which a series of holes of difierent diameters are drilled. In the fuli rich position the largest hole will be in r nunication with the starter circuit and provide the richest mixturc.

Potroi is drawn from tho fioatchamber via a vertical drilling adjaccnt to the central rnain feed channcis. throogh the starting device and into the throttle body on the almospberic sidc of tho throttle piąte. Simultaneously. tho cam on the starter lever will open the throttle beyond the normal idlc position. according to the setting of the fast-idle step screw. to provide the fast-idle speed when the motor 1$ cold.

As the dasfr-board control on the instrument panel is gradually released, srrullcr holes will provide the peirol feed from the float-chambor. tbereby progressivcly weakening the mixture strength to the point where the control is pushed fully homo and naturę Strer.gth will be govcrncd by the setting of the orifice adjusting screw and tho idle speed determincd by the setting of the throttle stop screw. Noto: The accelcrator pedał should not be depressed when starting from cold on cithor type.

Idling

Thcrc i> no separate idling Circuit in the Strombcrg " CD " carburetter, and the fuel is providcd by the jet orifice 19. the amount being contra’led by the setting of the orifice adjusting screw 13 and the speed of idle by adjustment to the throttle stop screw 3 whkh limits the closure of the throttle when the foot is off the accelcrator pedał.

Turmng tlve orifice adjusting screw clockwlso dccrcascs the mixlure strength; antl-clockwise will enrich.

Normal Running

With the opening of the butlerfly throttle manifold depression is '.ransferred (via a drilling 25 in the air valvc) to the chamber 24 which is sealed from the main body by the dlaphragm 16.

The pressure diffcrence between chamber 24 and that cxisting in the borę 26causes the air valve to lift. Ihus any incrcase in engine speed or load will enlarge the effcctiye chokc area Since the air valve lift is proportional to the weight of air passmg the throttle 27. By this mcans air velo:ity and pressurc drop across the jet orifice romain approximately constant ensuring good fuel atomisation at all speed s.    -

As the air vilve 13 rises it withdraw; a tapered metering needle 29 held In tho ł*>e of liie air valve by tnc sc/ew 10 from the jet orifice 19 so that fuel flow is incrcascd relative to the greater air flow.

Tho metering noedle is a variable and is machincc to very dose limits to prcwide a mixturc ratio for all speeds and loads In linę with engine rcquirements as determincd by cxhausiivo tests on bench ar.d rcod by carburetter specialists working in collaboration with the engine manufacturcrs.

Aceeleration

At any point in tho throttle rangę a temporarily richcr mixture is needed at the moment the throttle is suddcnly opened. To provide this. a dashpot or hydraulic dampor is arranged inside the hollow guide rod 17 of the air valve.

The rod itsclf is fillcd with suitaWe oil to within a of the end of the rod in which the damper 14 operates. When tho throttle is opened, tho Immediatc upward motion of the air valvc ls resisted by this plungcr. For that short time the suction or depression at the jet orifice is incrcased and the mixturc is cnriclied.

For all normal rcquiromonts engine oil SAS 20 is suitabte unless tl>e car manufacturcrs rccommend sorne varation from this.

As a generał rule the same grade of cii may bo usod in the dashpot to that which is used in the crankcase of tho engine.

The downward movcmcnt of the air valve 18 is assisted by tho coil spring 15 and/or a wcighted air valve.

ADJUSTMENTS Setting the Idle

Two adjustmenls are employed when regulating the idle speed and mixturc. and thefollowing procedurę should be adopted in setting the throttle stop screw 3 which Controls the speed. and jet adjusting screw 13 which determines the quality of air-fucl mixture entering the cylinders.

Remove the air cleancr and dampor and hołd the air valve 18 down on to the brkfge 28 in the throttle borę. Now screw up the jet adjustment screw 13 (a coin is ideał lor this purpose) until the jet is felt to comc into contact with the underside of the air valve. From this position turn down the jet adjusting screw three turns. This establhhcs an acoroximatc jet position from which to work.

Run the engine until it is thoroughly warm, and obtain by mcans of the stop screw 3 an idlc speed of sorne 600/650 r.p.m,

The idle mixture wili be correct when tnc engine beat is smooth and regular, and by careful and gradual adjustment of the jet adjustment screw 13 the correct position will be determincd.

As a chock. lift tho air valve a vcry smali amount (&•) with a long thin scrcw-driver and listen to the effcct on the engine. If the engine speed rises apprcciably, the mixturc is teo rich and, conversely, if tho engine Stops. the mixture <s too weak. Properly adjusted. the engine speed will either rcmain constant or fali slightly on lifting the air valve.

Adjusting and Synchronising Twin Carburetter Installation.

Looscn the clamping bolts on the throttle spindlc cooplings between the two instrumonts. Next. unscrew the throttle stop serews to perroit the throttles in cach carburetter to elose completely, then screw in the throttle stop serews 3. to the point where the ends of the serews are just contactir.g the castingi. From this point, rotate the stop serews I} ccmplcte turns each. to open the throttles an equal amount and provide a basis froin which finał speed of idle can be set.

Noto: Emuio fast-idle sciew Is elear of cam. otherwise incorrect synchronising will rcsult.

Rcgulatc the jet adjusting serews 13 as deuiled under the hcading '* Setting the Idle " i.e. throe turns down from the point where the jet orifice comcs into contact with the bose cf the air valve 18.

Check that both cold start lcvcrs are fully off against the stops with dashboard control pushed in. Adjust coupling and control wiro as noccssary.

Start engine and warm-up to normal running temperaturę. Check synchronising of throttles with suitablc instrument, or ” tubę to car " methed. at each intakc. then tighten clamping fcolts on throttle coupling.

Set the throttle stop serews to give requircd idle speed, turning each screw an cqual amount. Make finał mixture adjustment with jet adjusting serews, turning cach a similar amount, until idling is cvcn as prcvicusly detailed.