bradford carb

[PhilDenson]

Hi there, Can anyone help with Bradford leaky carbureter please?

[Tony Fearn]

Phil lives close to me, but under lock-down I can't go to visit him.
He's had a Bradford in the past and has now acquired another one.
The one he has now I think is a CB model, but there's a CA engine installed.
The carburettor on the CA is a Zenith 30VEFH, just as the pre-war twins.
For some reason it keeps dripping petrol, and he's tearing his hair out (of which he still has plenty, even though he's north of 80) because he doesn't know why it's dripping.
I've provided him with another similar carburettor and the problem still exists after fitting it.
He's had a word with our Chairman (and Bradford Registrar), and a well-known Jowett expert who answers the phone at JCS, as well as our Comp. Sec. but still the problem will not go away.
I'm at a loss as well.
I really could do with a concerted effort from the world-wide JowettTalk fraternity, especially (but not necessarily) you Bradford buffs, to suggest what the matter could be, and how to eliminate the problem.
Please don't just read this then ignore the plea.
Phil's nowhere near losing 'the will to live', but perhaps we can help.
Tony.

[David Kemp]

Depending on where it is leaking from a few ideas i learnt the hard way are.
The banjo fitting & the pipe it is connected to need to be perfect.One of mine had been slightly bent & could not seal.
If it is flooding either put a washer under the needle valve. Or check the fuel pump pressure.

[Forumadmin]

Does anybody know if the 30VEFH has a gasket between body and float chamber like the 30vm?

zenith.co.uk does not have one listed but I suggested to Phil he phone them.
I went through all the possibilities with Phil by phone based on my 30VM experience!

He says fuel stops when putting finger on valve and pumping manually.
He says the float floats freely. He has tried different thickness washers.
I suggested he take out the filter and pressure regulator he has fitted.
I suggested he check the pressure relief valve in the petrol pump.
He says the petrol leaks when pumped manually. I think he said from around emulsion block.
He has changed emulsion blocks and the whole carb.
But as we know both carbs could have same problem!!!!! But I suspect petrol pump.

[BarryHarding]

If it stops with your finger on the needle valve , but the float will not stop it, then it has to be a faulty needle valve.
It is also possible the pump is providing too much pressure, I have found all this is very critical on a Bradford, but very careful checking and assembly will usually fix the problem.
Barry

[Forumadmin]

Thanks Barry from the rolling hills of Western Australia. Getting that Bradford ready for the trip over to the east coast?

[AlanBartlett]

Is it dripping while running? Are all the pipes to the carburettor ok? Any weak solder joints on the banjo or slightly loose pipe clamps? Sometimes it looks like it would appear from the carb, but could be seeping from somewhere else. How about squished fibre washers where the pipe bolts up to the carburettor? What are the threads like where it tightens? How about flooding from the mixture screw. There is a hole in the top, if one of the jets is blocked it will push it out through there. Interesting its happening on both carburettors.

Alan

[PhilDenson]

Many thanks for all your help, comments and advice all gratefully received. I have already checked all these points but have done it all again. The Zenith carb people do not have any information on the 30VEFH. According to them from memory there is no gasket fitted. Their records start at 30VM.Totally puzzled and still got plenty of hair to rive out!
Tried removing the fuel restrictor and in line filter to no avail.
Will keep on trying but if someone else has any ideas I will try them too.

Only other thought is to go environmental all electric but I don't want to go down that route I don't think it will suit the Bradford image! Ha Ha!

Phil.

[AlanBartlett]

Have you had it running with the leak? Or just manually primed up with the primer/handle. I've had a look at both the weasel and the saloon which also shares the same carb. You can pump it up manually. Just prior to starting the carburettor will appear to leak. Once its started the "leak" stops. My guess is its a rather basic system, until its sucked down into the engine actually being used it will creep out. I've also found a Zenith Hints book which I shall get uploaded for a peruse.

[Tony Fearn]

I've also found a Zenith Hints book which I shall get uploaded for a peruse.

Thanks Alan.
I've forwarded the scan to Phil.
I was surprised it was over 22Mb.
Tony

[PhilDenson]

Hi Tony and Allan,

Many thanks, I have printed a copy of the book for which I am very grateful and will look at it in more detail tomorrow . The last time it ran it leaked but just at the minute it doesnt seem to want to start. Back into the garage Monday!

Thanks. Regards.

[Keith Clements]

Please send scan to me and I will put in Library.

[Tony Fearn]

Hi Keith.
I've just done so.
Tony.

[Keith Clements]

THE ZENITH CARBURETTER co.. LTD.

40-44, Newman Street, LONDON, W.l.

Telephone: MUSEUM 9106-7-8-9. Telegrams: "Zenicarbur, l:'honc, London."

British Empire Representatives and Agents Abroad

AUSTRALIA

Facto1·y Represent c.t iv e: ]AMES THORNELL, Esq., P.O. Box 2673 EE. Sydney, N .S.\V.

Wholesale Agents ancl Stockists:

Victoria-KE eP Enos. & Wooo P'l'Y., L-eo., Batman Street, \\'est Melbourne. Queensland-MAR'tiN WH.SON Bnos ., LTD., 284, Adelaide Street, Brisbane. New South Wales- BENN>:'I"l' & Wooo, L'l'D., 284, Pitt Street, Sydney, N.S.\'v', South Australia- L>:Nuoc, L'•·o., 123/5, Flinters Street, Adelaide.

-. West Australia- HARRIS SCA!n'B & SANDOv>:I<, L'l'D., Hay Street, Perth.

Tasmania- \\1. C. GBNDEHS P'l'Y., L'1'D., 53, Came ron Street, Launceston. (Also at Hobart.) NEW ZEALAND

Factory Rep-resentat -ive: }AMI·:s 'l'HORN LL, Es<J., P.O. Box 577, \Nellington.

Wholesale Agents and Stockists:

Wellington- JoHN CHAMBERS & SoN, l;rD., C. l'.O. J3ox 463, \\/e llington. Dunedin-JoHN CHAMB:ttRS & SoN, L1'D., St u art St reet, Post Box 109, Dunedin.

Christchurch- JoHN CHAMBERS & SoN, L·•·o., 200/202, St. Asaph St., P.O . Box 466, Christchurch. Auckland-Mol'OR SP.E;CIALI'l'IES, LTD., 80/82, Anzac Avenue, Auckland.

SOUTH AFRICA

Factor y Representative: BEGBIE I-IuNTI;R, J•;sq., P.O. Box 551, Cape Town.

Wholesale Agents ancl Stockists:

Cape Colony- East London and Border Terl'itories- BARNF.S GARAGE, Oxford St., East London.

Western Province--ATKINSON'S MoTORS, ] 'I'D., 51, Strand Street, Cape Town. Natal and Zululand-Du ROSt;'s AuTOMOTIVJ-; SuPPLn:s, 103, :'ltanger Street, Durban.

C. DuROSE & Co. P'l'Y., LTD., 210, Commercial Road, Pietermaritz)mrg.

O.F.S. and Basutoland-A't'KINSON 'S MoTOR GARAGES, L·ro., Bloemfontein.

Transvaal- AuTOMOTIVE SuPPLIES (}OHANN;I;snunc ) PTY., Ll'o., 17", Rissik Street, Johannesburg.

AuTOMOTIVE SUPPLIES (PRETOUIA) P'l'Y., L>·o., 281, St. Andries Street, Pretoria. WEST AFRICA

Nigeria-THE UNITED AFI<ICA Co., LTD., Motor Department. vV>:S'!' AFUICAN MoTORS, L'l'D.

NIGERIAN MoTons, L•rn

Gold Coast- 'l'IIE UN !'HD AFRICA Co., L>'D., Motor Devartment. Sierra Leone- THE UNI'l'F.D AFRICA Co., L'l'D., Iotor Department. Gambia- Tm: UNI'l'ED AFRICA Co., L>'D., Motor Department. INDIA AND CEYLON

Factor)' Rep,-esentative: G. VIN'l', c/o G.P.O., Bombay, India.

Whole sale A ge nts and Stockists:

Bombay Presidency-MEHTA & Co., Opera I-Iou se, Tram Terminus, Bombay. Delhi and District-UNil'ED TRADING Co., Kashmir 'Gate, Delhi.

Calcutta-HowRAH !VIaToR Co., Norton Buildings, P.O. Box 2263, Calcutta.

Madras-CHAMP ION Au·roMOlliL£5, Mount Road, 1\-Iadras. Lahore---]uLLUNDUR MoTOR AGENCY, Nila Cumbad, Lahore. Ceylon- vV AI.KF.R, SoNS & Co., L1'D., P.O. Box 166, Colombo. STRAITS SETTLEMENTS AND BORNEO

Singapore- BORNEO Mo'l'ORS, Orchard Road, Singapore.

Penang and Perak- Cu!N L':oNG & Co. (MAt.AYA) LTD., Church Street, Penang. Malaya States- H ocK II01& Co., 15, Batu noad, Kua l a Lumpur, F.M.S. ZANZIBAR AND PEMBA ISLAND-

'l'HJ·: nAs'l'EUN lVfO'l'OR GARAGJ.:J Engil)eers, P.O. Box 67, Zanzibar.

JAMAICA- ]liU 'I' I S II JV!O'I'On CA R Co., L'I'D., 111, Harbour Street, Kingston. CYPRUS- D. J . 'Jh;M,\D I·:s, F,sq., P.O. Box 104, N icosia.

SUDAN-CoN'l'OM I CJIALUS DAnKe & Co. (1929), L'ro., P.O. Box 221, Khartoum . BAGHDAD- vV . J . (o K>:H, J·;sq., New S treet, Baghdad.

IMPORTANT POINTS

HE correct working of the ZENITH Carburetter can only be assured when it i s not tampered with in any way,; the jets niust not be reamered o ut or hammered up, and the hints

ZENITH 3

and the cylinders, and arrangements are made to run i·he e ngine

unti l hot o n petrol , when it can be switched over to pa ra ffin.

. The secret of success with paraffin is to properly vapori se the

that a proper vapo rise_r is

which are given in this booklet must be strictly adhered to.

A ZENITH Carburetter, proper ly fitted , can be tuned up in a few hours, but when badly fitted the tuning up becomes

impossible.

The number stamped under the main jet and compensating jet

corresponds as a rule to the bore of the jets in hundredths of m / m.,

i.e., main jet that is marked 125 has an orifice with a theoretical

diameter of 1.25 m / m., and one that is marked 85 s hould measure

0.85 m / m . All jets are ca li brated on a B. & B. Mark II . flowmeter,

but sometimes customers s peci ally request that the jets sh ou ld be

stamped w ith th e numbe r corresponding to their flow in cubic

centimetres of pe+rol per minute, on the Mark II . f l owmete r. In this

case, however, th e jets arc s peciall y mark ed w i th c/c after th e

number, and we s hall be pl eosed ro se nd a li st of equiva l ents to an

i nter ested customer.

All th e jets are very ca refully ga u ged to pass a certai n q uanti ty

of fuel in a stated time, a nd t h e refore two jets bearing the sa me number pass exactl y the sa m e quantity. It is thus essential that

they should n ot be a l t ered und e r any circ um sta nces.

The standard markings on our jets run in fi ves, so that a SIZe larger jet than 80 wo ul d be 85, a nd a size smaller 75, and so on.

The · higher the number the larger th e jet.

For the nam es of the different parts of the Carburetter, please

ref er to the sectional drawings on pp. I 0 and I I.

NATURE OF THE FUEL USED

The ZENITH Carburetter is suppl ied already adjusted for use w ith petrol spir its of densities between 700° a n d 750°.

Carburetters thus ad ju sted may therefore be u sed with be n zo l e without altering the setting. The l eve l, h owever, will bo lowe r in t h e Carburetter ow in g to th e in c rease of d e n s i·ry, bur lhi s diff e ren ce in

level is necessary a nd p reclud es, as a rul e, M y modifi ca ti o n of

the jets. Never weight i·h e iloal or m n k o a lt era ti o n s to the level

when u si n g h eavy spirits, but on e s i zo s m a ll e r jo l s m a y ofte n be used to advantage.

It is of the utmost importance wh e n u s in g co mparatively hi gh den s ity spir i r, s uc h as Be nzol e , to in s t a ll u ve ry eff icient heatin g appara iu s in ord e r to proper l y va po urise i·h e h eavier fuel.

Paraffin ca n a l so be employed with th e Ze nith Car bure tt e r·, providing an effici e nt vapor i ser i s fit·red betwee n the Carburo tt o r

fuel , an d in this respect it may be said

one in which th e inlet pipe virtually pa sses . inside the exhaust p r pe.

TAKING DOWN THE ZENITH CARBURETTER

THE FLOAT CHAMBER.- In the vertical type of Carburetters p ull ba ck t h e sp ri ng butto n w hi ch holds the cover in place, and carefully lif t off the latte r toget he r w ith the needle and balan ce weights. The edge of the cove r is milled in order ·rhat a good gri p may be obtained, but care s h o uld be taken to avoid bending th e needle. After the cov e r i s removed it ,i s eas y to take out the f l oa t by means of the needl e, o r a h oo k ed piece of wire, which is placed down the centre hol e. '

Ver y ofte n it i s f ound t h ere i s a s mall pi ece filed ou t of the edge of the f l oat chambe r cove r, and this has to coincide either with the scr e w hol d i ng the s pr i n g o r e lse the bod y of the Carburetter. Care should be taken when rep l a cing t he float chamber cover that this cut out portion is in the p ro per position. After inserting the needle in the float, it woul d be fo und that if the cover is tu r ned ro u nd i t will generally fall i nto t h e co r rect pos ition.

In some of +he horizontal t y pes of Carburetters the centre knob is unscrewed o n e turn , wh e n o n turning the cover round a little it comes away quite easi l y.

THE CHOKE TUBE.-This i s a cylindrical piece of metal placed

i n the body of the Carburetter, a round the jets, to cause the rush

of air necessary to form a good m ix ture and to regulate the quantity of air entering t h e Carburetter.


In the vertical type of Carburet­ te·r s t h e t hrottl e and spind l e must be taken o ut before t h e choke tube can be removed . To do this, remove the set screw w hich fixes the throttle on the spind le, take t h e t h roHie between t he thumb and first finge r and pull th e spind l e out. After this, loose n t h e pressure screws h old i ng the choke tube in p lace, and it will then genera lly come out quite eas i l y by turning the Carburetter u ps ide down .

Fig. 1

If this is not the case owin g to the choke tube or the Carburette r havi ng received a blow, it can be removed as s hown in Fig. I. First unscrew the main jet and the main jet cover, and then place a metal washer, a h a lf pe nn y , f o r ex ample, against the choke tube, and force it out with a thin rod pa ss ing through the main jet hole as shown. Care s h o ul d be tak e n n ot to damage the thread of the main jet and cover.

When replacing the choke tube take great care to make sure that the narrowest internal part is downwards, and that the groove around it rests on the ledge cu t for that purpose in the body of the Carburetter (Fig. 2). Tighten the pressure sc rews to hold the ch oke tube in place, and then put back the spindle and throttle. It is importa nt that the latter should be

Fig. 2- Sec tion sh o win g !> Osi t i o n of p roperly refitted, and when it i s

ch oke tube in V e rti ca l Ca rhurctte rs. . correctly replaced the lower edge

when fully s hu t s h ou ld ju st cove r the outlet from the slow-running tube, and the number stamped on the throttle s h ou ld be uppermost.

In t h e h o- rizontal type of Carburetter it is mu ch easier to tak e. out the choke tube. First of all unscrew the dome air intake or air strangler on the back of the Carburetter, then take out the main jet below, and after this 'unscrew the main jet cover, when it will be found that by turning this to one si de the choke tube will pull out of the Carburetter with the main jet cover. The choke tube is put in at the same time as the jet cover.

TAKING OUT THE JETS.- A jet key i s se n t out w ith eac h

Carburetter for th e pu r pose of taking out th e jets.

The hexagonal nuts be l ow th e jei's mu st bo fir•, l re m oved by m eans of a n ordinary spann e r, w h e n th o jets cn n bo un sc rewed by the speci a l jet key.

When replacin g the jets mak e s ure th a t- th ey h a ve a washer on them, and that it i s well dow n on th e sh o uld e r.


We can suppl y a s peci a l box span n er for re moving the plugs und er the jets. Price 2 /2 post free.


ZENITH 5

TUNING UP THE . CARBURETTER

Each Carburetter is se nt out fitted with a main jet, compen ­ sa ting jet, ch oke tube. and main jet cover best s ui ted for that particular e n g in e acco rding to our experience with same, and t h e combination of these four parts constitute w hat we call a " settin g:"

Th e Ze nith Carburetter being automatic in principle, it is necessa r y, in ord e r to obtain all the advantages it affords in respect of flexibility, powe r and econo m y that the Carburetter should be ad ju sted to s uit th e particul a r engine on which it is to work. We would also mention that th e Carburetter need only be properly ad ju sted o n ce and for all, as it cannot vary o r alter of i ts ow n accord .

If we receive correct d et a il s of thengine when a Carburetter

is ordered, the setting th at we put in the Carburetter as a rule i s the

correct one, beca u se this h as been carefully tested on similar cars in the past, and therefore g e n e ra lly a Carburetter wit h this setting

s hould not be altered.

If such a Carburetter does not give good running , it is very likely the faults are not due to carburatio n a t all, but owing to so me ot her part of the engine being o ut of adjustment.


As, howeve r, individual e gines vary s l ig h tl y , we think it advisab le to make a few remark s o n t h e general ad ju stment of the Carburetter.

Fig. 3 Fig. 4 •Fig. 5

Th e Zen ith is adjusted by determining the correct si zes of

ch ok e tube (Fi g. 3), main jet (Fig . 4), compe n sa ting jet (Fi g. 5), and by ad ju stm e nt of th e slow- running tube (Figs. 8, 9, I 0).

Nor ally speaking, the purpose of the choke tube is to measure the correct quantity of air e ntering the Carburetter and to regulate the velocit y of same.

Th e main jet exe rts most inf l uences at high speed, whi l st the compensator corrects the irreg ularities of the main jet at low speed, and therefore has great in rlu e n ce at low pulling speed such as when climbing hills, pickin g u p, et c.

Most of the Carburetters s u p plied by us are fitted with an open main jet cover (Fig. 6), b u t somet imes in the case of old two-cylinde r engines, where th e s u cti on stro ke occurs a·r irregular intervals, we fit a dome cap as Fi g . 7.





Fi g. 6--Sec tio n o f ope n ca p. Ji'ig. 7 S L·c li on of d o m e cap.

The standard open main jet cove r i s s u p pli ed with a n inte rnal diameter of 3.3 m / rn., but sometim es a n improve m e nt i s o bta ined on small engines in acce l eration by fiHing a m a in jet cov e r with a s li g htl y sma ll er orifice , say 3.2 m / m. o r eve n 3.1 m / m.

Th e actua l size of the main jet cove r i s f ound stamped on one side of the hex agon at the base of sa m e.


A fuller d escription of the princip l e of the Ze nith will be gladly sent on applica tion.

ZENITH 7

If the Carburetter has been properly fitted in acco rdance with the instructions previously given, and contains th e setting we recommend for the engine on which it is to be used, we m a y now proceed to sta rt the engine.

STARTING UP.

With a cold e ngine the best method is as follows :-

Close th e Air Strangler. Open the throttle a very slight amount until a sort of s u cki ng n o i se is heard when the engine is cranked over.

This in d i ca tes th a t th e petrol is being sucked t hrough ·rhe slow- running tu be, and if th e i g nition and valves are i n order th e engine should start immediate l y.

As soon as the engine h as started ·r he air strangler s h o uld be opene.d s l ightly , and aft e r th e engine has been running a few minutes and has becom e s lightly warmed up, i·he strangler can

probably be openeci fully.

Should the e ngi ne s ta rt rea dily, but stop of its' own accord shortly afterw<J rds, it gen e rally s h ows that the throttle is not opened

quite sufficiently.

. If the throttle is open ed too much, it will always cause diffi. culty in starting. (Further hints on starting will be found on page 13.)

SLOW RUNNING.

Sever·al s ys+ems of slow- run ning ad jus tment have bee n applied to the Zen ith Carburetter since ii·s ince ption, but we give bel ow the latest methods that have bee n in u s e since 1 9 14,

The adjustment of the slow r unning depends on setting i·he throttle in the correct position to o btain t he correct quan tit y of mi x ture, and t hen obtaining th e pro per qua l ity of mixture by adjustment of the slow-running tube. A stop screw is provided o n the throttle lever, and this shou l d be so adjusted that the engine, when warm, runs at its lowest speed without stopping on sudd e n

deceleration. '

This will regulate ' the speed at which the engine will run, but it may not be running quite even l y. ·

J·t is then that the slow-running tube should ' be ad ju sted as pe r the instructions given below. ·

It i s important to· note that sl ow running which is appa ently a qu es tion of · persona l satisfaction has considerable effeCt on

accel era i-i o n.

It i s th e refore necessary to regu l ate the slow running of a n e ngin e as carefu ll y as possib l e. · ·

Fig. 8 -Slow·runni ng d evice (vertica l Car· burette r s ABC- DEF).

Fig. 9 -Slow·runnin g dev ice (h o ri zontal Ca r· burett er s H- HA).

Fig. 10- Slow-running d evi ce (horizont a l and ve rtica l Ca rburett e rs).

La t est t y pe.

If, however, the adjustment portion " G " is un sc rewed the distance is increased between "A" and "G," and th e s uction on the former will become less, and naturally the mixture will be weaker.

The size of the male conical jet "A" is stamped on th e bottom of the tube, a nd if it is found that with . "A" and " G " sc rewed close togeth e r th e mixture is still not rich enough, then a larg e r orifice "A" i s needed, and this can be supplied. Likewise, if with the a dju s·rm ent un screwed two or three complete tu r ns the mi xture is still too ri c h, th e n a s maller jet is necessary.

In the t y pe as pe r Fig. 8 it i s necessary to remove the complete tube from th e Carburetter, wh e n the part " 0 " can be unscrewed or screwed up.

Holding the part " B " in the left hand and screwing the part " 0 " with the right hand in a clockwis-e direction makes the mixture richer, and anti-clockwise weak e r.

With the type Fig. 9, whi ch is only employed with horizontal Carburetters, it will be necessa ry to first of all remove the cap "N," and then turn the screw " B " to the left or right by means of a

screwdriver.

The same direction appli es , i.e., clockwise-richer, and· anti­

clockwise- weake r.

In the latest t y pe , as pe r Fig. I 0, the adjustment can be made whilst th e e ngin e is running by m ean s of the knob "B." After

The slow-running tubes, Figs. 8 and 1 0, are only pu s h ed into the

Carburetter and held by means of a screw.

Consequently, to remove same, it is onl y n ecessa ry to l oosen the screw and pull the tube out.

If it is rather tightly fixed the tube can be p ri sed up by means of a screwdriver, the point of which is in serted und e r th e kn o b " B " or under the nut " X" when this i s l oose n ed a nd u sin g so m e convenient part of the Carburetter, such as th e throttl e boss , as a fulcrum.

In the type Fig. 9 the tube is screwed into th e Ca rb u rette r and has to be removed by means of a special h exa g on a l key that is supplied with the Carburetter.

The method of regulating the stre ngth of th e mi xture with -1-he slow-running t e,is by .lteri,g the relative position of the male and female cones A and G.



The male cone "A" takes the form of a conical jet. It will be readily understood if the female cone " G " is put close to this jet, the suction on same will be greater and consequently a richer mixture will be given by the slow-running tube.

loosening the nut " X," th e kn o b is screwed in a clockwise direction to make the mixture rich e r a nd vi ce versa, then when the correct position has been found, ca n be locked in place by means of the

nut "X."

There is no standard positi on for the adjustment of the slow­ running tube as this varies on ea ch engine, but as a rule it is some­ where between the fully closed pos ition, which is when the female cone touches the male cone-which, of course, is the richest position

-and two complete turns unscrewed. ,I

After the slow-running tube has been adjusted it may be necessary to make another small adjustment to the stop screw on the throttle lever.

Flang

\

Adjusting knobof

Section of Vertical Carburetter


0

11iddle portion of slow­

running devi ce

sl ow-running devtce '\ Butterfly throttle

Th.-ottle spindle \

'--- - - -

Throttle stop

ad justing screw

Screw holdin g choke t ube

Choke tube

S trangle r lever

Bottom portion of

slow-running dev-ice

)fain jet coY er

Strangl e r spi nd l e Strangler flap fi1ain jet

Plug· under main jet

Plug under compen ­

sa tin g jet


Midd le portion of slo w­

r unning device

Strangl er cowl

Float-n eed l e

Sp ring for float­

chamber cover

Float-chamber cover

Counterwei ght

Counterweight spindl e

Float-needl e collar

Bottom portion of

slow-running devi ce

Float-needle sea ting Filter adapter Petrol union nut

Petrol union nipple


Section of Horizontal Carburetter

Scre w holding slow­

running devi Ce

Float-chamber cove r

Float-needle

Spri ng knob

Sp rin g for {]oat-chamber

cover N Screw fixing cover sp ri ng m Counterweight spindle z

Counterweight

Float -n eed l e collar -1

I

Float

Float-needle sea tin g

Petrol union nut

Petrol union nipple

Filter arla pte r

Filter tube

Stra n gler lever

Adjusting knob of

slow-running dev i ce

Throttl e spindl e

Flange

Throttle screw

Butterfly throttle N

m

Choke tube z

1\ia in j et cov e r -1

Mai n j e t I

CorApensating jet

Plug und e r main j e t

Plug under compensating

jet

Filter tube

GENERAL RUNNING
In the following pa ges we deal specifically with certain defects in the running, and th eir re m edies, but the following general remarks on tuning will no d o ubt be u seful.
Choke Tube too Large.- The effect of this, as a rule, is that acceleration is ge n e ra lly ba d under all conditions.

Choke Tube too Small.- ln this case the engine will generally pick up ve ry well, but m ax imum s peed cannot be obtained owing to the choke tube restrictin g the quantity of air entering the Carburetter.
Main Jet too Large.- This, as a rule, causes the petrol con­ sumption to be heavy, t h e running to be woolly and irregular at medium and high speed s.
It is sometimes found th a t the same speed is obtain ed with two jets of different sizes, and t h e s mallest should always be chosen on the score of economy.
Main Jet too Small.- Thi s will cause a loss of power and popping back when acceleratin g.
The engine will a l so run harsh and perhaps a little on the warm side.
Compensating Jet too La rge will cause sluggish acceleration and woolly runnin g a t l ow speed .
. Compensating Jet too Small will cause missing on acceleration,
< and possibly knocking wh e n pulling hard at low speed.
HOW TO WRITE FOR PARTICULARS RE TUNING-UP, ETC.

It is absolutely esse ntial to give the following parti c ul a rs :- ·

Z ENITH 13

COMMON .RUNNING TROUBLES AND THEIR REMEDIES

DI FF I C ULT STARTING WHEN COLD
Chiefly ca used by the throttle not being set in t h o correct position. (See Remark on page 7.)

An e n g in e is most easily started from col d in l h o f oll ow in g mann e r :-

Ci ose th e a ir strangler, shut the throttle righ t bock to th e stop screw, i.e., the position in which the engine run s s l ow l y o u t of gear when warrn, and then with the ignition switched off, c ra n k th e engine over half-a-dozen times or so either by h a n d or w i t h the self-starter. Then open the throttle between a r!l' tm t o i\ t h of an inch, and still keeping the strangler shut, switch on th e ig n itio n. It will then generally be found th a t the engine will start q ui te readi l y. The object of cranking the e ngine over with the igni ti o n off i s two-fold . In the first place it frees the engine, and in th e seco nd place primes it with suitable m i xture for starting.
The best position is g e n e ra lly with the throttle open a s h a d e more than th e best slow-runnin g position when warm. A f ew trial s will generally s how th e best position of the throttle for ea sy sta rt i ng, and a mark s h o uld be m ade on t he hand control so that th e throttle ca,n a l wa ys be p ut in thi s pos iti o n.
In ve ry cold w ea th e r sta rti n g i s sometimes facilitated b y s lightly flooding the Carburetter. .
No Air Strangler fitted ·or existing one not closing properly.­ We can supply a loose stran g l er f or fitting to earli er types of Carburetters. See that the stran g l e r control permits the complete closing of this.
I . H.P., mak e a nd year of car.
2. Number of cylinders.
Slow-Running Tube choked up-. Jet "A," as shown on page 8.

Thoroughly clean out the

and and
3. Bore c;tnd stroke of same.
4. Number of Carburetter used (pl ea se me nti o n all letters figures stamped on the SIDE of th e fl oa t c h a mber).
5. The present setting (numbe r o n m a in jet, compensator choke tube) .
6. Whether a heating device is in sta ll ed, if so, of which
Slow-Running Tube adjusted oo weakly.-Turn the adjustment knob in a clockwise direction to give a richer mixture.
Air Leakage between Carburetter and Cylinders.- Go carefully over all inlet pipe joints, valve caps, sparking plugs, etc.
The inlet valve guides may be worn and allowing air leakag e between the stems and the guides. .
Magneto Retarded too much, •or Inefficient at low r.p.m.- This

type.

Also please state any other particulars which are likely to help us when replying, such as existing troubles if any.
must be ca refully checked. .
Sparking Plug Points too far apart.- Very often puttin g th ese slightly closer together greatly improves starting,

DIFFICULT STARTING WHEN HOT

Slow-running Tube adjusted too richly.-Adjust the knob in an anti-clockwise direction .

Carburetter has been flooded or air strangler closed.-An excess of petrol will cause difficult starting when the engine is hot.

Throttle no·+ open sufficiently.-Adjust the stop screw to open the throttle a shade more.

BAD SLOW RUNNING

It is presumed that the s l ow-r unning tu be and stop screw have been carefully adjusted in accorda nce with the remarks on page 7, but slow running is still bad.

Air leakage between Carburetters and the cylinders.- Go over the points mentioned above.

If vacuum-tank, servo brake or windscreen wiper are fitted, go carefully over the air connections.

The magneto is inefficient at low speeds or adv 11ced too much.

- Have this properly exa mined.

Plug Points too far apart.- Try these with a slightly sma ller gap. Inlet Valve Tappets badly or unevenly adjusted.- Very carefully

sei· these.

ZENITH 15

ENGINE STOPS ON DECELERATION Slow-Running Tube choked up.-Take out and c l ean .

Slow-Running Tube adjusted too weakly.- Set ·rhi s to g1 ve a

richer mixture.

Inlet Valve Tappets unevenly adjusted.-These must be very carefu lly set.

Throttle Loose on its Spindle.-Take the Carburetter down and tig hten t h e l ock ing screw which holds the throttle to the spindle .

Stop Screw on Throttle Lever improperly adjusted. -Set thi s sc rew so t h a i· the thrttle always returns to the best sl ow- running posit i o n.

ACCELERATION IS BAD OR THERE IS HESITATION IN PICKING UP SPEED

Inlet pipe or passages insufficiently heated, so that when the engine is running slowly petrol vapour condenses on the inside, at1d when the throttle is opened for acceleration this liquid petrol is sucked into the cylinders, causing the mixture to be too rich, and hesitation occurs.

etc.

Uneven Compression in Cylinders.- -Have the valves ground in,

Inlet Pipe or Passages not sufficiently heated.-'yV h e n the

Arrange to moro o f f i cien il y heat t h e inlet pipe or passa ges.

Compensating Jet too lar ge or too small.- Try different sizes






engine is running slowly, the petrol vapour will condense on the inside of the unh eated passages , .causing irregular s low running.

Impro ve the heating by fitting a hot air p i pe or cleaning ou+

the jacket if one exists.

Throttle Spind l e or Throttle W·orn.- After a numbe r of years of use, the throttle spindle and the throttl e wear, which m ay upset the slow running. In this case it is a lw ays best to se nd back th e Carburetter to be thoroughly overhaul ed and m ade as n ew , for which we have a prompt and efficient repa ir d epart m ent.

Engine stops of its own accord after running slowly for a certain time.-Where a vacuum tank i s employed it is sometimes found that each time the vacuum. tank funct i ons, the eng ine stops. This is due to a charge of rich gabeing drawn from the autovac tank through the suction pipe, thereby upsetting the mixture supplied by the Carburetter. Also, where a Servo brake mechanism is employed . it will often be found that the er\gir\e will be liable to stop when the brake functions. Obviously there is no cure for either of

these two things by Carburetter adjustment.

of compensa+ing jets.

Choke Tube too large. Try one s i ze s maller c hok e i·u be without altering the jets.

Slow-Running Tube not correctly adjusted.- Very carefully set this as described on pages 7 and 8 to give the best mixture for even slow running.

It is sometimes preferable to set the engine to run a shade faster than is absolutely necessary out of gear as this will sometimes give a cleaner pick-up.

Uneven Disi-ribuHon of the Mixture.- Due to the shape of the inl et pipe or passages being incorrect or too large.

If this is suspected, the best thing is to send us a sketc h of the induction system for our criticism and advice.

Magneto retarded too much, •Or inefficient at low speed.- Have this carefully seen to.

Plug Points too far apart.-Adjust these more closely. Uneven Compression.- Have the valves gra.und in .

LACK OF SPEED Main jet too small.- Try a size larger.

Choke Tube too smaii.- Try a size larger, with also a s1ze

larger main jet. ·

lgnifi.on Retarded too much.-This is of very common occurrence. Have this carefully timed.

.Insufficient Supply of Petrol to the Float Chamber.-Due to dirt in the petrol pipe, or to one of the filters being choked up.

Thoroughly clean out the petrol system, see that there is a good flow through the pipe when the union is disconnected at the C rburetter end.

Vacuum Tank not working properly at hig1h speed, causing a shortage of petrol. Have this carefully tested .

Insufficient lift of the Needle Valve in .the Carburetter, causing

a shortage of petrol at high speed. Unsolder the coll ar on the .

float needle and move it a shade nearer to the point, but not sufficient to cause constant flooding.

Loss of Compression in the Cylinders.- H ave the va l ves care­

fully examined.

Pre-ignition caused by faulty Plugs or Dirty Engine.- lf the engine knocks after a certain speed this is probably the case.

Air Strangler on Carburetter sticks in a partially closed position.

-This would restrict the amount of mixture en·rering the cylinders,

and cause loss of speed.

POPPING OCCURS IN THE CARBURETTER AT SPEED OR WHEN CLIMBING HILLS

Shortage of petrol ·due to the reasons mentioned in the previous paragraph.-Go carefully over these.

Jets too smalL-Fit one size larg er m a in jet to stop the popping at high speeds, or one size larger compe n sa ro r if it occurs when climbing h i lls.

Sparking Plugs faulty, causing pre-ignition.- Try a different type of sparki ng plug, preferably with a sh orter reach or a heavier electrode.

Valves not clo·sing properly.- Make s ure that the tappets are properly set with sufficient clearance, and that the valves do not stick or bind in their guides w hen the engine is hot. .

The Float Chamber Cover on the Carburetter is loose.-This may cause the float needle to stick when the vibration is great and prevents a proper supp ly of petrol to the fl oat chambe r.

See that th e spring holding the float chamber cover is in position.

ZENITH 17

EXCESSIVE PETROL CONSUMPTION

llho mixturo is too rich, and in this case try a sma ll e r m a in jet and th e n ,, '.1!11l ll o r compe nsa tor. If carburation is at fault, then wh e n s m ,dlnt jots are fitted in the Carburetter not o nly will the cons1mrl ion b u red u ced , but the running improved. If it i s foun,d th ar ir i•, n o r possible to fit either one size smaller main jet or one size s mllll or co mpensator without· immediately losing power, it shows th n r th o mixture i s about as weak as it is possibl e to get it, and co n sequ e ntly the excessive consumption cannot be due to

ca rburation.

Consequently the following items should be examin ed:-

Loss of efficiency in the Engine.-Check the compressi on a nd make sure the ignition is properly advanced, as retarded ignition is a very common cause of excessive petrol consumption.

Brakes Bindinq.-See that it is possible to push the car easily with the brakes off. ·

The Engine is ne·w and stiff.- Never expect any car to give a

reasonable consumption until it has run about I ,000 to I ,500 miles

to get properly run in, and all the bearings are quite free.

Petrol Leaking.- Make sure the Carburetter is not flooding. If so , correct thi s as per th e remarks in the following paragraph.

Make sure petrol i s not leaking anywhere between the

Carburetter and th e tank.

Make sure the consumption is really excessive. Do not guess the mileage per gallon of your car, but carefully check this on a run ·over give-and-take roads of at least 50 miles.

CARBURETTER CONTINUALLY FLOODS OR LEAKS Petrol runs from t h e air intake of the Carburetter until Petrol

Tap is turned off.- The level in the float chamber is too high.

Unsolder the collar o n the float n eedle and move it a shade further

from the point.

The needle is bent and therefore sticks in its guide before seating properly.

In this case, the best thing would be to fit a new needle.

The Float punctured and containing petroL- The quickest thing

i s to get a new float from us, but a temporary repair can be effected by immersing the float in hot water, which will vaporise the petrol and drive it out through the puncture. Thi s should be marked a nd filled with a spot of solder as soon as all the petrol i s ent irely

evaporatE)Q,

Dirt has settled on the needle seating.- Th o roughl y cl ea n the seating a n d the float ch a mbe r of all dirt and grit. Lightly grind the needle on to its sea ting wi t h a l i ttl e metal polis h but nothing coarser.

Under no circumstances whatever must the needle valve be ground in with emery or any other coarse paste. Neither should the needle be forced on to its seating with a screwdriver, but slightly ground by turning round with the fingers.

The Float Needle or Seating worn.-- lf th ere is a ridge o n th e needl e f ace or the sea tin g s h ows a bevel on the ed g e of same, then th ese pa rts s ho u ld be rep l aced .

Th e colla r o n t h e n e w float need le must be very carefully set and t hi.s ca n onl y be don e o n th e Carbu retter .

The cor rect l eve l for t h e petrol i n t he floa t chamber cor respo nd s t o 3 m / m below th e top of t h e main jet cov e r.

O n t he h orizontal Ca rburetter t h is ca n be see n on the eng i ne by un screwing t h e a ir d o m e at the back, ta ki n g o ut the m ain jet and replac i ng th e pl ug.

Th e petro l ca n i· h e n be seen in t h e m a in jet cov e r .

O n t h e ve rti ca l l ype it i s n ecessary to dismo u nt t h e Ca r burette r f ro m t h e eng i ne and r i g it up on a bench wit h a spare ta n k .

Th e m ain jet i s th e n ta ke n out an d p lug repl aced u n d erneai·h , w hen th e lev el in t h e m ai n jet cove r ca n be seen by pee rin g down the top of the Ca rburette r.

In the ca se of bot h t h e ve r ti ca l and hor izontal Ca r b u rette r t h e co rect adju stm e n t f o r th e l evel is obtai n ed by m oving the co ll a r o n

t he float needle.

. If this is put n earer to th e poi n t t h e l ev e l becom es h i g h e r and v1ce versa.

The coll a r is a dri vi ng fi t o n t h e n eed l e , and i s sol d ered in its fin a l pos ition.

A sold e red collar can easily be re moved by h ea t i n g the needle and collar in a gas flame, when th e coll ar ca n be tapped up or down.

Petrol continues to leak from the Carburetter although the level is correct.- This is probabl y du e to o n e of th e p lugs or screws not being tight. Go carefully over the plug s un de r the jets, the main jet cover and the various screws outside th e Carburetter, and tighten these all up prope rly and mak e sure th ey h a ve sound washer s .

I '

il

ZENITH 19


Petrol drips from th e Ca rburetter for a short time after stopping the engine and th e n dries up of its own accord.- This petrol is s im p ly that v apo u r w h i c h h os co ndensed on the inside of the inlet pipe and pass r1 gos w h e n !·h e e ngine has been running. As soon as

· the engin e i s s i O!J f 'Od , t h e s uction is released, and this liquid petrol runs ba ck t h ro u 9 h th e Carburetter, giving one the impression of

l ea kage o r fl ood in g.

I t i s go n oro lly ca u sed by the inlet pa ssag es being insufficiently h ca i od, o r f o th e mi x tur e for slow running being ra th e r too rich. A s a ru l e , n o n oti ce need be taken of it.

Gen e ral Remarks on Flooding and Leaking.- Wh e n ever a

Ca rb u retter i s l eaking and can be spared for three days , it i s qui c ker

and better to send it back to us for rectification. We h a ve a very pro mpt and efficient Repair Department.

Once more, never grind in a needlwith emery or other paste­ it will ruin both fhe needle and seating, and you will never be able to get a tight joint.

ENGINE OVERHEATS AFTER A SHORT TIME AND WATER BOILS

This is very seldom due to carburation, but sometimes if the mixture is too weak it will cause the engine to get rather hot.

Try larger main jet, and if this gives no improvement and there

i s a good s up p ly of petrol to th e float chamber one can be certain t hat the overheating is not due to carburation. They should therefore

l ook to the cooling system, the fan belt and more especially the timing of the magneto and valv es, as wrong adjustment of these is

the most common cause of overheating.

KNOCKING

The engine commences to pink or knock as soon as it is called u pon to do any hard work.

Engine Dirty.- Have this decarbonised.

Ignition too far advanced.- Retard this slightly.

Pre-ignition.- Due to faulty plugs. Try a new set of plugs, preferably with heavier electrodes or a shorter reach.

Mixture too weak.-Fit larger main jet and make sure that the petrol supp l y to the float chamber is in order.

POPPING OCCURS IN CARBURETTER ON SUDDEN DECELERATION

Slow-running tube partially choked up.- Ciean this out thoroughl y.

Slow-running tube adjusted too weakly.- Adju st this to give a sl ightly richer mixture.

Air leakage af fhe joint between Silencer and Exhaust Pipe.­ R ectify this.

[Keith Clements]

Manual now in Library and searchable Archive.
https://jowett.net/forum/viewtopic.php?f=99&t=5914

But also included below are the pages and OCR of them in HTML format so they are searchable using the JT search box.
To do a search of the pdf version use the archive search available to members.
The update of the Archive is currently a manual process so documents in the JowettTalk Library may not immeadiately be available in the Archive.
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