zenith carburetor model 29 service manual

7/15/2019 Zenith Carburetor Model 29 Service Manual

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B u l J « ~ t i n ." ' n o Z-2l!i-B

ZENITH 29-SER IES CARBURETORS

OP:ERATION AND SERVICE

The Zenith 29 Series is a downdraft carburetorwit h a concentr ic float bowl design. This designassi st s in th e proper metering of ai r and f uel t o

t he engine, wi thout flooding, when th e vehicle isoperated on extreme angles. I t is a "s ealed" and

Figure 1

"balanced" ca rburetor in that all air for f uel bowlch a m be r v en ti l a ti on and idling mus t come

th rough the ai r cleaner. Air cleaner r estrictionshav e a minimum influence on f uel-air ra tio. Adouble venturi is employed to aid in t he completevaporization of th e f uel. Th e power jet andaccelerating pump systems ar e operated by engine vacuum and are completely enclosed andprotected f rom dirt. Th ese auxiliary je t systemsare t o provide t he extra f uel needed for certainopera tions.

INSTRUCTIONS FOR ADJUSTING

ADJUSTMENTS:

1. The th rottle stop screw (1), F ig . 1, should bescrewed in (clockwise) against th e stop pin

(2) t o hold t he throttl e j us t slightly open.Ad just th e t hrot tle stop screw to obtain thedesired idling speed of t he engine .

2. Th e idling adjust ing scre w (3) should be f rom1 to 1112 full turns off it s seat . Ad just th eidling ad j usting screw to obtain smooth idlingwhen engine ha s become thoroughly warmedup . Turning t he screw in (clockwise) cut s offair, making th e idling mix ture ri cher ; whilet urn ing it out (counter - clockwise) admitsmore a ir , making t he mixtu re leaner .

I f i t becomes necessa ry to tu rn t he screwin to less t han 1/2 tu rn off th e seat t o obtain

good idling of th e eng ine , it would indicateeither an air leak or a r estriction in th e flowof fuel for idl ing. Look for air leaks at th e

manifold flange; at carburetor t hrottle bodyt o intake gasket, and at carburetor bowl tocove r gasket , due to loosened assembly screwsor damaged gaskets. A badly worn throttleshaf t will produce sufficient air leakage toaffect t he idl ing mixture.

Dirt or other foreign matter in th e idli ngjet calibration will r es tr ic t t he flow of f uelfor idling and affect the mixture. I f the idlingjet becomes completely clogged, it will be impossible to run the engine at idling spe ed regardless of adjustment of th e idling adjustment screw.

3. Some models of th is ser ies ar e supplied with

a main jet adjustment which is installed inplace of plug (4) , Fig. 1. Turning th e needleclockwise cuts off fuel making th e mediumand high speed mixtures leaner. The needleshould be adjusted to give highest manifoldvacuum (or highes t R. P. IV!. on a ta chometer)for a set-throt t le position . (This is usuallyabout 11/2 f ull turns (counter-clockwise) fromt he seat .) I f engi ne is equipped with speedgovernor, set the throt tle to hold th e enginespeed j ust below the governed speed whilead ju sting th e main je t ad ju stm ent. I f adjust ment is se t t oo lean, t he engine will lackpower and t he fu el economy also will be poor.I f set too rich, t he engine will be sluggish

and t he fuel economy poor.

STARTING:

Open t he throttl e abou t one-qu ar te r . Pull th echoke control all t he way. Step on th e starter.As soon as t he engine sta rts, push t he choke control in about one-third of th e way and as th e engi ne warms up , continue t o pu sh it in graduallyuntil t he choke valve is wide open.

Note: I f t he engine, after running satisfact orily, suddenly ceases to perform properly, donot change th e carburetor ad jus tment . Look overt he intake manifold, ca rburet or flange gasket s,t hrottle, choke, and f uel connections . Make sur ethat t hrot tle and choke open and close correctlyand tha t f uel is reaching t he carburetor in asteady stream . Do no t change carburetor ad justments until other causes of trouble, including

ignition, have been inv estigat ed . Changes inadjustmen t should be necessary only with changein fuel or climate.

MODEL IDENTIFICATION

TYPE-DOWNDRAFT:

STYLE 29- Throttle and choke sh afts parallelwith pr iming plug loca t ed under a ir in ta ke.



FUEL SUPPLY SYSTEM:

Th e function of t he float is to maintain t hecorrect level of f uel in t he fuel bowl under alloperating cond itions. Gasoline passes throughthe fu el valve seat into th e fuel chamber. When

t he amount of fu el re aches a predetermined levelit causes t he float to ri se and pu sh the fuel valveneedle agains t it s seat, stopping t he inflow ofga soline. When t he eng ine is ru nning and fuelflows f rom th e fuel. chamber to th e met ering sys

tem j ets, t he fu el va lve assumes a position wit hjust enough opening to supply th e requiredamount of fuel to keep t he fuel level constant .

The fuel bowl is located in a central position

di rect ly above t he thrott le pla t e. The mai n discharge je t and met ering well are located in th e

center of th e f ue l bowl.

STYLE 29-B-Th rottle and choke shafts a t righ tan gles with priming plu g locat ed on lefthand side of t hrott le body .

STYLE 29-BB - Throttle and choke shafts atrigh t angles with priming plug located onrigh t hand side of t hrottle body.

STYLE R-Built-in governor .

STYLE W- Vacuum oper a ted pump and powe r

jet.STYLE X-Flange nex t size larger than standard.

Size Nominal Throttle Bore Plange SizeDesignation Size Diameter S.A.E. St d.

11 1%1" 1.535- H I" 1%,"12 1112" 1.653 -1 B" 11/:!"14 1%" 1.889-1H" 13) .1,"16 2" 2.165 -2 3 " 2"

IDLE JET

IDLE JETCALIBRATION

AIR PASSAGE

'DUNEEDlE VALVE

SEAT

Fig u re 3

IDLE

DISCHARGE

PORT

METER iNGWEll

IDLE ADJU5TlNG NEEDLE

IDlE . ~ ! ! l - ! ! ~ - - - - t - - - - - t : FEED HO tE

IDLING SYSTEM:

This system consists of an id le discha rge port

loca ted in th e side of th e thrott le body, an idl e

jet to meter fuel, a vacuum passage connectingwit h t he idle port , an idle ad just ing needle, an

idle air in t ake passage, and a pe rmanent idle ai rbleed. At id ling speed th e t h rottle pla t e is slightlyadvanced f rom a compl etely closed position leaving about one-half the area of t he idle dischargeport revealed to th e suction in th e engine man ifo ld. Th is suction is tr ansm itted to the idlingjet through a passage running th rough th e a irin take, fue l bowl, and fue l bowl cover. Fuel f romt he fue l bowl chamber flows throug h t he mainjet into th e mete ring well. Fu el fo r idling flowsfrom th is well t hrough th e idle f eed hole at t helower end of t he metering well t o th e idle well tobe metered through t he idle je t. As the f uel

leaves the idle jet and enters the vacuum passage leading to the idle discharge port , it is mixedwith air admi t ted f rom th e air in take t hr ought he idl e a ir passage in an am ount measured byt he perman en t idle ai r blee d at t he upper end oft he idl e a ir intake channel. An additional variablevolume of air is adm it ted past t he. idling adj usting needle and it s seat. Th is emulsified mixturet hen passes through t he idle vacuum pas sage tobe discharged into th e engine manifo ld at theidle discharge port. The permanent idle a ir bleedcalibrat ion is to prevent f uel from being syphonedint o th e intake manifold.

Air for venti la tion of th e fuel bowl is providedt hrough a pitot tube. Th e pressures in t he f uelbowl and air entr ance a re "balanced" by vent ingt he f uel bowl from the air entrance.

fU El VALVE 5EATUEl INtO

Figure 2

OPERATION

METERING WEll



POWER JET SYSTEM:

This part of the high speed system consists

of : a power je t valve which restricts th e flowof fue l to the power jet calibration; a vacuumcontrolled p is ton assembly fo r operating thepower je t valve; and an accelerating pump checkvalve located in th e fuel bowl controlling th e pas-sage from th e fuel bowl into th e acceleratingpump cylinder. The manifold vacuum is com-municated through opening "E " and th e vacuumpassage to th e vacuum pis ton. Under normalpart throttle operating conditions, th e vacuumpiston is held in th e upper position and th e powerje t valve is closed. When the throt tle is openedwide, or when th e load on th e engine is increased

HIGH SPEED SYSTEM:

This system consists of: a main venturi con-trolling th e maximum volume of air admittedinto th e engine; a secondary venturi to increaseth e suction on th e discharge jet; a main jet whichregulates th e flow of fuel from th e float chamberto the main discharge jet; a well vent jet whichmaintains uniform mixture ratio under changingsuction and engine speeds; and a main dischargeje t which delivers th e emulsified fuel into th eair stream. As the throt tle is opened, th e suc-tion at th e priming plug diminishes, but the in-creased volume of air entering th e engine createssufficient vacuum in th e secondary venturi todraw fuel from th e metering well up and overinto th e discharge tube . Th e flow characteristicsfrom th e main discharge tube are influenced byth e size and number of holes used in th e side ofth e metering well. Ai r from th e float chamber,which is vented through a channel to th e pitottube in the air intake, is admitted to the outerside of th e metering well through th e well ventjet.

POWER JET

fUELPASSAGE

VACUUM PISTONHECKVALVE

ACCELERATING PUMP SYSTEM:

This system consists of : a pump cylinder; avacuum controlled pump piston to discharge thefuel; a check va lve located in th e fuel bowl tocontrol th e passage from th e fuel bowl into th epump cylinder ; an air vent check valve locatedin th e fuel bowl cover ; and an accelerating jetlocated in the center of th e main meter ing wellto meter th e rate at which fuel is discharged .

The leng th of the pump stroke determines th eamount of fuel used .

Sudden throttle openings wiII cause th e mani-fold vacuum t o drop, allowing th e acceleratingpump spring to force th e pump piston downwardin t he cylinder. This forces th e fuel through theangle passage to the accelerating jet. Fuel issupplied to the pump cylinder through the checkvalve in the fuel bowl. The pump check valve inthe bowl serves two purposes : I t permits a sup-ply of fuel to reach th e pump cylinder but closeson th e down stroke of th e piston , preventing th efuel in th e cylinder from being pushed back into

the main jet fuel in the well and provide a fullpower mixture.

When t he throt tl e posit ion, or th e road andload condition, allows th e manifold vacuum to rise

above a predetermined point, the pump assemblyis l if ted and th e power jet valve closes, permittingthe carburetor to deliver an economy mixtureagain.

due to road condit ions, to a point wh ere th emanifold vacuum drops below a predeterminedpoint, th e pump assembly drops and holds th epower je t va lve open. This permits fuel to flowthrough th e power jet calibration to supplement

METERING

WELL

PERMAN£!,<'TAIR BLf ED

MAIN VENTURI

Figure 4

WEll VENT JET

MAINDISCHARGE

JET

IDLE-MAIN

JET FUEL

SEPARATION

AIR

BLEEDHOLES



the bowl. To preven t the accelerating jet f romflowing a t all t hrott le openings above idle, th eair vent check val ve is placed between the acceler -ating jet and pump cylinder above t he fue l level.At steady part throt tle positions, with t he pumppiston held up to t he top of its st r oke, no pres-

Figure 6

AIR SHUTTER VAl VE

(CHOKEI

Figure 7

POPPET

VALVE

SPRING

CHOKE SYSTEM:

This system consists chiefly of : a va lve mount-ed on a shaft located in t he air entrance andoperated ex ternall y by a lever mounted on t heshaft. The choke system is used t o restrict t heair ente ring the carburetor and to increa se t hesuction on the jet s when starting th e engine.The choke valve has a poppet va lve incorporatedin it s design , wh ich is controlled by a sp ring.

AIR VENT

PASSAGE

CYLINDER

ACCELERATING JET

Air CHECK VALVE

m ! ! l ! - ~ ~ ~ ~ ~ - ANG LE PASSAGE

VACUUMPISTON

sure exis ts on the f uel in t he pump cylinder.Under t his cond ition t he air vent check valve will

be open and ai r ente rs t he pa ssage connectingthe pump cylinder and accelerating j et and prevents fuel from flowing through the jet. Thepressure on th e fu el cr ea t ed by the down strokeof th e pump piston causes t he air vent checkvalve to close aga in st i ts seat to prevent fu elfrom being discharged back into t he bowl t hroughth e air ven t passage.

The poppet valve opens au tomatically when the

engine sta r ts . This adm it s a ir to avoid over -ch ok ing or flooding of t he eng ine . Th e chokevalve is complete ly closed when star t ing t he engine and then mu st be instantl y opened part wayby th e operator when the engine begins to run.As th e engine wa rms up the choke valve is graduall y advanced to the wide open position by th eopera tor to supply t he leaner mixtu res required.

SERVICE AND REPAIR PROCEDURE

(A) IDENTIFY CARBURETOR

(a ) Check the numbers on metal ident ificat ion discr ive ted to top of float bowl cove r ag a inst carburetoroutli ne speci ficat ion cha rt . Th e insi de number nextt o th e ri ve t is t he Zeni th outline assembly number ,

a nd the one nex t t o t he outer edge of th e di sc is th evehicle manufacturer 's.

(B) DISASSEMBLED VIEW

(a ) Th e disassembled view will ide nt if y t he var iouscomponent par ts a nd show the ir relation t o as-sembly . Use th e disassembled view wi th the identifyi ng part numbers to ident if y a nd loca te partswhen performing t he di sassembly an d r eassemblyoperations.

(C) SUGGESTED REPAIR PROCEDURE

1. Remove id ling ad j usting screw ( 1) and spri ng (2) ,using finger s.

2. Remove bowl to air in take assem bly scr ews (4) an dlockwashers (5) usin g a sc rewdriver .

3. Lif t fuel bow l a ssembly (28) clear of ai r intakea nd tu rn it up side down .

4. Remove bowl to in take gasket (32).

5. Remove discharge t ube (30 ) and gaske t (29) usingse r vice t ool C161-10 ( 0 1' a 7/ 16" wre nch).

6. Turn bowl r ight si de up and re move cove r assemblyscrews (3) and lockwashers (6 ) using a screwdr iver .

7. Remov e bowl cover assembly (8 ) and turn upsidedown to

8. Remove ga sket (16) a nd pump assembly (13).

9. Remove floa t a xle (15 ) using a screwdriver to pus hthe axl e through th e slotted end of the hingebr a ck et and the finge rs to r emove it the rest of th eway.

10. Remove float asse mbly (14) a nd f ue l va lve needle(10).

11. Remove f uel va lve seat (10) an d gasket (9) , usin gservice too l C161-85 (or a Ih" screwdriver).



Figure 8

12. Remo ve pump r efill check va lv e ( 12) and di sc (11) ,using se r v ice tool C161-5.

(a ) In ser t t ap er ed thread en d into the va lve bodyand screw in (coun ter-clockwise) until tool isfirmly a t tached to th e body; th en ra i se th esliding weight up sha rply against th e sto p ba ra few times to r emove the part. Be ca reful toav oid screwing the tool t oo deeply into th e

valve body a s it may damage th e a ir ven tcheck valve sea t that is pr essed in to the coverdi r ectly abov e this poin t. I f t he hole in th evalve body becomes enlarged, g rind a li tt le offth e end of th e tool so it will sta r t to g r ip th ebody sooner .

One end of the stop ba r is made t o in stal l asimilar valve in anot he r model of carburetorbu t should not be used to in stall th is valve.

C161-22 se rv ice tool ca n al so be used a s anex tr ac tor only fo r th is valve.

NOTE: Do not remove th e ai r vent check valv e sea t, th efloa t hi nge br a cket , the channel plugs, or t he identification

disc.

13. Remove idli ng jet (19), usin g finger s onlv to lift itout of the bowl ca sting. .

14. Remove well vent (22), using service tool C161-80(o r a 3/1 6" wrench ) .

15. Remove acc elerating jet (17 ), using a sma ll screwdriver .

NOTE: I f meter in g well t urn s wit h jet pr oceed withitem 16 and remove j et afterwards. '

16. To r emove meteri ng well (18) , inse rt a piece ofsma ll r od about 4" long in th e di scharg e je t channel a nd pu sh th e metering r od well up fa r eno ughto provide finger hold to r emove it .

17. Remove P?wer jet va lve (20 ) a nd gasket (21 ),USIng ser vice to ol C161-121, bein g ca ref ul to havethe to ol properly cente r ed on th e va lve head .

18. Remove bowl plug (or main jet a d justment if used )(2 5) and gas ke t (24) , using a %" wr ench.

19. Remove ma.in jet (26) an d gasket (27 ), usinga screwd r iver Inserted throug h th e opening fromwhi ch the plug (25) was re mov ed.

20 . Remove pu mp check val ve assembly (23), usin gC161-123 ext r actor.

(a ) In ser t t ap er ed thread end into t he val ve andscrew in (coun ter -clockw ise ) until t he t ool isfirmly attached to th e va lve body, t he n st ri kethe ben t end with a ham mer squa r ely a nd

sha rply a f ew times to pull th e valve out . I ftool pushes the va lve disc out , be su re t he discis no t lef t in th e ca rburetor channel.

NOTE: Do not remove th e channel bushings or channelplu gs.

21. Turn t he intake assemb ly (31) up side down a ndremove th rott le body to a ir int ake ass embly screw s(66) and lockwasher (65), usi ng a 7/ 16" endwr ench to loosen a nd a sc rewd r ive r to remove.

22. Lift throttle body (57) clear of the int ake (31)and at t he same t ime note carefully that t he holesin t he ga sket lin e up with th e channels in t heth rottle body an d th a t there is a locating pi n t opr ev en t a ssembling th e thrott le body an d ai r in takeincorr ectly.

23. As you lift th e vent ur i assembly (56 ) an d gasket

(55 ) cleat' of th e a ir intake, not e t hat th er e is alocat ing boss on the side of the venturi to hold thevent ur i in th e correct posi ti on ; a lso note that th ega ske t blanks off one cha nnel in t he intake body .

24. ':1'0 r emov e the air shutt er ret a in er screws (54) , itIS nece ss ary fir st to file off th e r iveted ends, thenr emove th e a il' shut te r r et u rn spri ng (if one isused), hold the a ir shut t er lever (4 2 ) in clo sedpos ition and remove th e scr ews.

25. Pu sh t he ai r shut t er (53) into t he intake body (31 )to remove it .

26. Remove shaft (3 5) and lever (43) a s a unit.

27. Not e th e a ngle at whi ch th e br acket (37 ) is a tta ched to the a il' int ake (31) , then remov e th e reta iner screw (40) , using a 1J:., " wrench.

28. Remove th e shaf t hole plug (34 ) an d gasket (33 ),USIng a 1J:., " wrench.

NOTE: Do not r emove pit ot t ube, a ir shut ter s top pin, ai rshut te r br a cket locating p in , or channel plugs.

29. Remove t he throttle pla te (63) , sc re ws (62), shaftand sto p lever as sembly (51), th rottle cla mp lever(46) , as fo llows:

(a ) Unscrew throttle s top scre w (47) until thr eaded en d is flush wi th lever (49) .

(b) Make match mark s with cente r pu nch or fileon th rott le body (57 ) an d al l lever s to act a s aguide to re a ssemble th ese pa rts in t he sameposit ion as removed.



(c) Loosen throttle l ever c lamp screw (45) andremove le ve r (46 ) from shaft (52).

(d ) Remove throttle plate screws (62) and pull ou tt he throt tl e p la te (63) .

NOTE: The t hre ad ed end of th e screws are riveted andmust be filed f la t before removal, to avoid b reakage o rs tr ipping o f thr eads in t he throt tle shaft.

(e) Remove t he t hr ot tle shaf t and stop lever as-sembly (51) from th e throttle bod y (5 7) .

30. Remove throttle shaft packing (59) and packingretainer (58) f rom t he throttle body shaft holes asfollows :

(a ) Screw a fine thread t aper t ap into packing r e-tainer until it is firmly seated .

(b ) Insert a l ong punch or rod through oppositeshaft hol e and drive punch against the end ofthe ta p until retainer is free of the body.

NOTE A: Do not disass emble th e throttle plate (63),throttle shaft and s top lever as sembly (51), throttle pack-ing (59) and packing retainer (58), from th e throttlebody (57) , unless the throttle shaft is worn, ben t or other-wise damaged or unless there is damage to an y of th eother component pa r ts of th e throttle body a ssembly.

NOTE B: The location of the pr iming hole plug in r ela-

tion to t he throt tl e p la te is extremely impor tan t for un i-form idling an d part throttle operation . To maintain auniform relation between th e priming hol e p lug and th et hrot tl e p la te, our factory assembles t he t hr ot tl e shaftand p la te in th e throttle body before dri ll ing the hole inthe body fo r th e priming hole plug, locating the hol e in adefinite relation to the throttle plate in each case . I t isreadily apparent from th e above that t hrot tl e p la te s andthrottle bodies cannot be interchanged indiscriminately.When it becomes necessary to replace th e throttle shaftor throttle plate , we suggest th e following routine :

(a ) Unscrew th e throttle stop screw to permitcomplete closing of the throttle plate.

(b) Hold throttle in tightly closed position andmark th e ins ide of the throttle body close tothe throttle plate with a st eel scriber.

(c) Using this scribed line a s a guide, replace th e

throttle shaf t or plate. I t may be necessary totr y more than one new plate to ge t one thatfits very close to the scribed line wh en installed.

(d ) If throttle body ha s to be replaced, we recom-mend obtaining a complete throttle body as-sembly including sha f t , plate, priming holeplug, etc., built to th e out line number on th eidentification tag. The part number is B12-outline number.

NOTE C: For Governor Type throttle body assembly, seeService Bulletin 263 or 264.

CLEAN AND INSPECT PARTS

1. Clean all metal pa rt s t ho roughl y w ith cl ea ni ngsolution and r in se in solvent.

2. Blowout al l passages in the fuel bowl cove r, fuelbowl, air intake, and thro t tle body.

NOTE: Be sure al l carbon deposits have been removed

from throttle bore and idle port . I t is advisable t o reverseflow of compressed air in al l passages to insure al l dirtha s been removed. Never use a wire or drill to clean ou tjets.

3. Float Assembly ( 14 ). R ep lac e float i f loaded withgasoline, damaged, or if float axle bearing is wornexcessively. Inspec t top side of f loat lever fo r wea rwhere it contacts t he fuel valve needle.

4. Float Axle (15). Replace if an y wear can be visual-ly de tected on th e bearin g surface.

5. Fuel Valve Seat and Needle Assembly (10). Rep lacefuel valve sea t and needle assembly because bothparts wea r and may cause improper floa t level.

6. Idling Adjusting Needle (1). In spect po in t of needle,th is must be smooth a nd fr ee of r idges.

7. Throttle Plate (63) . Insp ect plate fo r burrs or dam-aged edges. Never clean a throttle p la te w it h abuffing wheel or a sharp in strument.

8. Vacuum P is ton Assembly (13 ). Both piston s mustbe free of scratches, burrs, and carbon, and must

fit cylinder at operating end within .003". Replace-ment recommended because extent of wea r cannotbe determined by vis u a l in spection.

9. Power Jet Valve (20). Replace this part becauseextent of w ear can not be determ ined by visual in -spection .

10. Ai r Shutter Chok e (5 3). Inspect fo r bends, burrs ,or damaged edges .

11. Air Shutter Shaft (Choke) (35). Check bearing su r-faces f or wear; see tha t shaft is straight.

12. Fuel Bowl Body (28). Examine pump cylinder a tlower end fo r ev idence of excessive wear, deepsc r at ches, or ridge s. Desirable clea rance betweenpump pis ton and pump cylinder at lower operatingend is .001", maximum clearance .003". Any clear-ance in excess of .003" will reduce acceleratingpump dis charge an d r esult in poor acceleration . I fabove condition is found , t he pump cyl inder shouldbe relined .

13. Fuel Bowl Cover (8). Examine pump cylinder forevidence of exce ss ive wear, deep scratches, ridges,or any mutilation of cy linder head. Desirable clear-ance between vacuum pi ston and cyl inder at upperoperating end is .001", maximum clea ra nce .003" .Any clearance in ex cess of .003" wil l a llow ai r orfuel to be di scharg ed int o manifold t hrough vacuumpassage leading from cylinde r head into throttlebody bore. Thi s condition re sul ts in poor idling,power je t and pump action. I f above condition isround th e pump cylmder should be relined .

NOTE: Some 29 Series carburetors have removable pumpliners which can be ser v ice d by ou r field organizat ion.Those that do no t ha ve r emovable liner s must be returnedto the factory for t he vacuum cylinder relining operation .

14. Throttle Shaft (52). Replace if shaft shows evi -dence of wear on the bearing surfaces .

15. Throttle Shaft Bushings (60). Replace if new shaftha s more than .005" side play . Any side play inexcess of .005" will allow dirt or grit to pass intoengine and r esult in exce ssive wear of cylinders,piston s, rings, etc .

16. Accelerating Pump Check Valve (23). Replace be -cause this part is damaged in removal, or extent ofwear cannot be determined by visua l in sp ection.

17. Gaskets: Replace a ll gaskets and fibr e washers ever ytime carburetor is disassembled.

18. Check Specifications: Venturi, Main Jet , Idling Je t ,Power Jet Valve, Accelerating Jet, Main Discharge

Jet, Well Ven t J et, and Fu el Valve Sea t.

NOTE: Do no t attempt to remove th e throttle sha f t bush-ings unl es s new bushings are availabl e fo r replacement.New bushings are under shaft s ize and re qu ir e r eamingwith a line reamer to fit shaft properly. Both bushingsand reamer must be available to successfully complet ethis operation.

(a) Screw a taper ta p 1/16" la rger than the thro t tleshaft hole into bushing until it is firmly seated .

(b ) Insert l ong punch or rod in opposite shaft holeand drive punch against end of ta p unt il bush-ing is fr ee of body.

(c) Repeat above operation to r emove bushing inopposite sha ft hole.



1. In stall throttle sha ft and st op lever assembly (51)an d throttle pl ate (63) in th e throttle body (57).Wh en throt tle plate is properly centered, tightent he r etainer screws (62) secur ely.

2. Rivet ends o f throt tle plate ret a iner scr ews, beingca r eful to avoid spr inging th e shaft . Use a pieceof ro d (about %" diameter) in a vise to supportth e sha f t , and a tinner 's ri veting hammer to ri vetth e screws.

3. In stall air shutter bracket (37) at correct an gle

(see it em 27 of di sassembly procedu re) using a12 "

wrenc h to t igh te n th e retainer screw (40) .

4. Replace a ir shut te r sha ft (35) and lever assembly(42) in a ir intake body (31) . In stal l a ir shutte rshaft with th read ed end of retainer screw holesdown (so screws can be in st alled f rom ou tside).

5. In stal l a ir shutter assembly (53) f r om inside thea ir intake, w it h relief va lve ste m up .

6. Hold in closed position to start r etainer sc rews(54) , the n snap the plat e shut a few times to aidin properl y cen te r ing it , th en t ighten th e reta inerscrews secure ly.

7. Install sha ft hole plug (34) and ga sket (33), usinga '12 " wre nch.

(d )

( e)

(f)

(g)

(h )

In st al l new th rottle shaft bu shings (i f r emov ed ) with Zenith C161-72-3 bushing driverfo r 5/ 16" shaf t hole bu shing, or Zenith C16172-4 bu shi ng dr iver for %" sha f t hol e bu shings.

Pl ace new bush in g on bu shing driver withtape r end of bu shing away f r om shoulder.

Sta r t bu shing in to shaf t hol e and drive it inuntil it bottoms, usin g a ligh t hammer.

Repeat th is oper ation to in stall second bushingin oppo site shaf t hol e.

Line re am th e t wo throt tle sha ft bushings,using special r eam er Zenith C161-71-3 fo r5/16" shaf t size, or C161-71-4 for 3jg" shaft size .

REASSEMBLY

NOTE: We suggest ti pp ing the ca rburetor on its side asan aid to ge t t ing the va lve a nd gasket into place moreeas ily.

16. Instal l acceler ating jet (17) in th e meteri ng well(18 ), u sing a sma ll sc rewdr ive r wh ile hol ding th emetering well with hand only.

17. Instal l metering well (18) w it h accelerating je t(17) in th e well cha nnel of f uel bowl (28) .

NOTE: Th e met ering well is designed to extend not mor ethan .015" above t he bowl cas t ing to in sure a good seal a t

that poin t when gaske t and cover are in pl ace.18. Instal l well ven t j et (22 ), u si ng Zenith tool C161-80

(o r a 3/16" wrench).

19. In stall idling j et (19) , using fing er s only.

20. To install pump r efill chec k valve (12) , place th evalve body , head down, on a flat metal block; pla cethe valve disc (11) in th e va lve body; place th ecover ca st in g (8 ) squa re ly over the va lve, t henstrike th e cast ing with a hammer (preferably arawhide mal let ) , t o drive th e cove r down ove r th evalve.

NOTE : Valve body sh ou ld be ju st flush w ith th e cast ing .

21. Repl ace fu el valve seat (10 ) and gaske t (9 ) , usingZenith tool C161-85 (or a %" screwdriver ).

22. P la ce fuel valve needle (10) in th e sea t ; hold th e

float a ssembly (14) in position and23. In stall float axle (15), using th e fingers to pu sh it

through t o th e slot and the handle end of a sc rewdriver to f orce it through th e slotted end of th e floathinge bracket. Th e float axle should extend aboutthe same distance on both sides of th e br acket .

NOTE: Th e float shou ld move fr eely on the axle.

24. Hold the cover and float up side down, as shown inFigu r e 9, to observe r elation of float to cover . Toobtain correct fuel level, w it h normal pump p res sure , consult float setting cha r t for Dimension A.Do no t bend t he floa t a rm , as new a nd undamagedparts will come wit h in the limits.

Figure 9

FLOAT SETTING CHART

25. Pla ce pump ass embly (13 ) in the pump cylinder .

26. P la ce th e bowl to cover gaske t (16) on th e fu elbowl (28).

27. Hold th e cover a ssembly (8 ) over th e bowl (28)and guide th e va cuum piston in to th e va cuum cylinder and th e idling jet (19 ) in to its channel, beingcarefu l to avoid damage to floa t and other pa r ts.

28. In st al l cover t o bowl as sembly screws (3) andlockwasher s (6) . Tighten them evenly and sec urely ,usi ng a screwdriver.

Dimension A1%6" ± ¥.!2"

10/16" ± ¥.!2"

± lh2"

Carburetor Model29-11,1229-1429-1 6

R. Pl ace th e ven tur i (56) in th e throt tle body, makingsure t ha t th e locating boss on t he side of th e

vent uri faces th e correct way to engage the notchin th e int ake body.

9. Pl ace th e body t o intake gas ke t (55) on th e throttlebody, making sur e that th e holes in the gasket lineup with channe l openings in the throttle body.

10. Pl ace the intake body (31) on th e throttle body(57), making sur e th a t th e loca ting boss on th eventur i eng ages th e slot provided f or it and thatth e locating dowel in th e throttle body eng age s th ein take flan ge properly. Hold parts together andtu r n up side dow n.

11. St a r t all four of the body intake sc rews (66) andlockwasher s (65) , t ighten down eve nly and secure ly .

12. In stall new pump check valve (23 ), using C161-124se rv ice t ool or sui ta ble flat-end punch.

(a ) C161-124 tool is machined at one end to fit th e

pump check va lve body an d is used with a lighthamm er to dr ive the valve assembly a s fa r inas th e shoulde r on th e t ool will permit . I f anord ina ry flat-end punch is used in st ead ofC161-124, be ca re f u l to avoid driving th e checkva lve fa r the r in than jus t below th e edge ofth e channe l opening.

13. Replace th e main j et (26) and was her (27), usinga sui tab le screwdriver inserted th rough th e openingin th e side of th e fu el bowl (28).

14. In stall bowl pl ug (or ma in je t adjustment) (25)and ga sket (24) , using a '12 " wr ench.

15. Replace power jet va lve (20) and ga sket (21),using Zenith tool C161-121, bein g care ful to haveth e tool pr operly cente red on the valve head .



RECOMMENDED SERVICE TOOLS

FOR 29 SERIES

I f th e ca r bu re tor is t o be used wit h a sa ndwich-t ypespeed governor, be su re th e hollow vacuum channel screw(64) is installed in th e carburetor flange, and that theflange gasket used ha s a hole th at coincides with thischannel.

29. I ns t al l discharge t ube (30) and ga ske t (2 9) inlower si de of bowl (28) , u sing Zenith tool C161-10(o r a 7/16" wr ench ) .

30. Place bowl to in take gasket (32) in position on th efu el bowl (28 ).

31. Pl a ce th e bowl assembly wit h ga sket on th e ai r inta ke (31) . Be sure th e channel bu shings ent er th ei rrespective channels.

32. Instal l th e assembly sc rews (4 ) and lockwashers(5) . Tighten them evenly and securely, using a

scr ewdriver .33. Install id li ng ad iu sti ng needle (1 ) and spr ing (2 ) ,

usin g finger s only .

NOTE: Before r eleasing th e ca rbu re t or f or se rvice again,set the mai n je t adjustmen t (i f one is used) at 1112 fullturns open ; se t th e idling adjustment ne edle (1 ) at onefull turn open; and set th e t hrottle stop sc rew (47) fa renough in against t he st op pin to hold t he throttle plateju st slightly open. These a r e preliminary adjus tm en tsthat will make star t ing easier when th e carburetor isinstal led .

C161-5

C161-10

C161-80

C161-85

C161-121

C161-123

C161 -124

CI61-72-3

CI61-72-4

CI61 -71-3

CI61-71-4

Pump Refill Check Valve Extractor.

Di scharge Tub e Wrench (7 /16" Hex. socket,

114" deep).Well Ven t J et Wrench (3 /16" Hex . socket,

%" deep).

Fuel Valve Seat Wrench.

Power Jet Valve Wrench.

Pump Check Valve Extractor .

Pump Check Valve Tool (to install) .

Bushing Dr ive r (for 5/16" sha ft ) .

Bush ing Driver (for 3jg" shaf t ) .

Line Reamer (for 5/ 16" shaft ) .

Line Reamer (for 3jg" shaft ).

~ ~ ~-z- -z- -z-~ ~

DETROIT 14, MICHIGAN

ZENITH CARBURETOR DIVISION~ ~"'AT'Olf CORPORATIOIt

696 HART AVENUE

Manufacturers of Zenith Carburetors and Filters

TillS S lJl'EIlSEIlES l J L L E T I ~ :'in. OF SEI'TEMIIEIl , 19VJ

J u ly, 1950 Prin ted in U. S. A.



ZENITH CARBURETOR RESTOROGRAPH

~/

76

EXPLODED VIEW

290 SERIES

DUPLEX

25 ~ 6 ,

J.,X>

\ ....""/ I 6 16 3 62

I . DISASSEMBLYDi sa s s embly consists of sepa ra ting the carbure to r in to two basic g roup s:fuel bowl and ai r intake -th r ottle body a nd the di sas sem bl y of each ofthe se groups . Use exploded illust r ati on above as a gui de fo r di sas semblyand r ea s semb ly .

2. CLEANING AND INSPECTION

Thoroughly clean al l meta l part s in Bendix Meta lc lene or Speedc lene . .Blow out all pa r t s an d channels with ai r pr e s su r e. In spe ct housi ng fo r

damage , exces s ive wear , bur rs or warpage . DO NOT CLEAN NONMETALLIC PARTS in Bendix Metalclene or Spe edcle ne .

3. REASSEMBLY

When r ea s sembling car buretor use e s senti all y the r ever se or de r from

di sa ssembly .

290 SERIES DUPLEX

KEY

NO. PART NAME

1 PLUG- F i lt er2 WASHER -f i lt e r Plug

3 SCREEN- F i lt er4 BODY- Union5 WASHER - Unio n Body6 WASHER - F ue l Valve Seat7 VAL VE & SEAT - Fue l8 JET - Idl e9 AXLE - f loat10 FLOAT11 WELL- Secondary12 VALVE_ Pump Check13 VENT - We ll14 WASHER - Idl e Co mpensa tor15 J ET - Idl e Compens a to r16 SCREW-C hok e Pl ate Stop17 HUT- Ch oke P lote Stop Screw18 WASHER - Moin J e t19 JET - Main

20 WASHER_Moin Passage P lug21 PL UG- Ma in Passage

22 PACKING-Choke Shaf t23 PLAT E- Sha ft Cover R.H.24 LOCKWA 5HER25 SCREW- P lat e or Brocket Assy ,26 SCREW- Choke Lever C lamp27 LEVER-Choke28 PLATE-Choke29 SCREW- Choke P lat e30 LOCKWASHER31 SCREW- Ventur i32 BEARING-Shaft Nee d le33 SEAL- Throttl e Shaf t34 WASHER_ Le ver Space r35 LEVE R & SHAFT- Throttle36 LEVER-Th rott le38 SCREW- Th rott le Leve r Cl amp39 LEVER- Th ro ttle C lamp

40 SP RING-Le ver Stop Screw41 SCR EW- Thrott le Lever Stop42 SHAFT_ Thrott le43 BODY- T hrottl e44 WASHER- Deg oss er P lug45 PL UG_ Degos se r Channel46 PLATE - Thrott le47 SCREW- Thrott le P late48 GASKET - Flange49 LOCKWASHE R50 SCREW- Bady to Bowl Assy .51 SCREW-Vacuum Channe l52 SET SCR EW- Th rus t Coller53 WASHER- Throttle Shaft Thr us t54 P LUG- Oega s s er Vac uum Channe l55 SPRING- Id le Ad justing Needle

56 NEEDLE - Idle Adj usting57 VENTURI58 J ET- Dis charge

59 WASHER- Dis cha rge Je t60 GASKET_ Bawl to Thrott le Body61 WASHER- Choke Sha ft Thrus t62 GASKET - Cover P la te63 PLATE_Shaft Cove r L. H.64 SHAFT- Choke65 BOWL- F ue l66 P LUG- Le ve l L ine & Bowl Dra in67 WASHER- Power Je t Va lve68 VALVE- Power J et69 JET - Acce le rat ing70 WELL- Mete ring71 GASKET -B ow l to Cove r72 PUMP ASSEMBLY73 BODY- Check Va lve74 BALL-A ir Vent Check75 COVE R- F uel Bowl76 LOCKWASHER77 SCREW- Bowl Cover



THROTTLE BODYASSEMBLY

1. Insta ll both th ro ttl e body dus t seals (33) wi th th in

edge of seals fa cing outwards , us ing finger s only.

2. P lace one thro tt le sha ft washe r (34) on th r ottlesha ft and in st a ll thro t tl e sha ft and lever assemb ly

(35) in thr ottle body . Align l ev e r s to match marksmade a t time of di s a s sembl y .

3 . Place th r ottle body assemb ly onbenchwith mount ing

flange up and faci ng id le ports on in si de of throttlebore s , then r otate th rottle sha ft to wide open

position.

4 . Ins tal l throttle plate (46) by in serting si de with

shorter di stance between screw holes and bevelededge in to shaft fi r st , wit h beve l on l onge r s id e

of plate up . Center thro ttle plate ; rota te shaft toclose position; start two throttle plate screws

(47 ) in place but do no t tig hten .

5. In stall other throttle pla te in same manne r. Makesure both pl a tes are properly ce nte r ed so that edge sfi t thro t tl e bore s closely , the n tigh ten a ll four

th r ott le pl a te screw s securely .

6. P lace thr ot tle shaft washe r (34) on e nd of shaftand insta ll thrus t collar (53 ) whil e hold ing thro tt lein fully closed po sition and ti ghten thrus t coll a r

set sc rew (52) .

NOTE: Shaft e nd pl ay shou ld not be more than.003 " and shaft shou ld r ot a te fr eely . I f thrust co ll a ri s too c lose , causing a "drag" when shaft is ro tated,s trike e nd of sha ft lightly wi th hammer to remove

" dr ag" .

7 . With th rottle plate s held in cl o sed po si ti on turnth r ot tle stop screw (41) IN (c lockwise) unti l screw

jus t contac ts stop pin. then turn stop screwIN 1- 1/2 turn s as a preliminary id le speed ad

ju s tm e nt .

8 . Instal l degasse r channel pl ug (45) and gasket(44), and al so in stal l 1/ 8" pipe plug (54) and

tighten secure ly .

9 . Ins tall idl e a djust ing need le (56) and spring (55),us ing finger s only. Turn id le needle in ligh tl y

agai ns t seat , then back out ne ed le 1/ 2 to 3/ 4 of aturn as a preliminary adjustment.

10 . P lace the bowl to body gasket (60) in po si t ion

on thro t tle body , then in stall two venturi as sem bli e s (57) and secure wi th venturi screw s (3 1) and

lockwa she r s (30) .

ASSEMBLYOF CHOKE INAR INTAKE

1. In stal l " C" washe r (61) on e nd of choke sha ftan d insert choke shaft in ai r intak e from sideshown. Align sh aft to match marks made at timeof disassembly , then rotate shaft to open position.

- 2-

2. Ins ta ll choke plat e (28) fr om inner s ide of sh afby s liding relief si de of c hoke plate over chokesha ft fi rs t with valve s tem towards vent tubeand the n work plate back in to s lo t of shaft. Cente

choke plate and r ota te choke to closed posi t ionThen s tart th re e choke pl a te screws (29) . Aligchoke for best closi ng and tighten choke platescrews .

3 . In stal l choke sha ft packing fe l t (22) in co unterbo r eand cover plate (23 ), cove r pl ate screws (25) an d

lockwash e r s (24) on side of ai r intake .

4. Ins tal l choke leve r (27) on choke sha ft and align

to match ma rk s made a t time of di sa s sembly and

then tighten c lamp screw (26).

5 . At opposi te si de fr om choke leve r, in stall cove rgaske t (62), shaft hol e cover pl a te (63 ), sc r ew(25) an d loc kwa sher s (24).

NOTE : I f choke adjusting screw (16 ) was loosene dthen it will be necessary to read jus t screw. Adjusscrew to close choke pl a te, as fa r a s pos sibl e wit hous ticking .

ASSEMB LY OF FUEL BOWL BODY

1. To install new pump c heck valve (12), ins e r t formed

end of C161- 124 tool in to che ck valv e body anddr ive va lve into counter-bore until top surface i ss li ghtl y below surrounding sur fac e of casting

2 . Install power jet valve (68) a nd fiber washer (67)in bottom of pump c ylinde r , using C161- 121 powe rjet valve wr ench .

3 . Insta ll two main jets (19) and fiber wa sher s (18)

tighten se cure ly .

4 . Ins ta ll two m ain je t passage plugs (2 1) a nd fiber

wa shers (20) in threaded openi ngs a t opposite sides

of fue l bowl.

5 . Insta ll two compen sating jets (15) and fiber wa she rs(14) in bottom of fuel bowl a t side opposi te pump

cylinder .

6 . Inve r t fue l bowl assembly and ins tall two discharge

jets (58 ) an d fibe r washers (59) , us i ng fi nger s tos ta r t jets and C 161 - 149 wrench to tighten jets.

ASSEMBLY OF THROTTLE BODY TO BOWL

1. With fue l bowl assembly i nverted , align matchmarks made prior to disassembl y on thro tt le bodand fue l bowl flanges .

2. Place throttle body a ssembly on fuel bowl assembly

and a li gn holes in throttle body flange wi th hol esin gasket and fue l bowl; then a tta ch th r ottle bodywi th throttle body assembly sc r ews (50) and lockwa sher s (49) . T ighten sc r ews evenly and se cure ly



P lace assemblies in upright position with bowl upand install three metering wells (11 and 70),f it ted together as a unit , in well cavi tie s of fue lbowl.

4. In stall two ac ce le r a t i ng je t s (69 ) , us ing fingers on ly;then install well ven t je t (13), u si ng a sc r ewdriver .

ASSEMBLYOF BOWL COVER

1. With bowl cove r in inverted po srtion , drop pumprefill check bal l (74) into place in cente r pass ageand in stall chec k va lve (73) wit h smootb side out .Use a flat end pun ch and a ligbt hamme r to drivecheck va lve into place flus h with the casting surfac e .

2 . Install fue l valve seat (7) an d fiber wa she r (6),

us ing 5/8" socke t wre nch .

3 . Install two idle je t s (8) and tighten firml y, using

small screwdriver.

4 . Place pump (72) in vac uum cylinde r . Push spr ingr e ta in e r di s c into rece ss i n c a s ti ng . using finger s

or flat s ide of sc r ewd r ive r bla de .

5 . Place fuel bowl cover gasket (71) in position onc ov e r , making sure holes in gasket coinci de withchannel openings ; then pla ce fuel valve needl e i n

seat .

6. Position flo at and lever a s s embly in hinge bracketand install floa t ax le (9). using finger to push axleth rough bracke t and bu shing to slo tt e d sid e of

hi nge bracket. Use handle end of sc rewdriver topu sh axle th rough slo tte d side of brac ket. Center

axl e .

7. F LOAT SETTING - To insure correct fue l leve l

in fue l chambe r , che ck di stance " A" from top of

float s to machined s urface of cover (no gasket)

1AL

with cover inverted. Th i s dim ension should be1- 5/ 8 " . To inc r e a s e or de c rease distance be tween

fl oat bodie s and machined surface , us e long no se

pl iers and bend lever cl o se to floa t body.

NOTE: 00 NOT bend, twist or apply pressure onthe flo at bodies . The flo at bodie s when vi ewed f romthe fr ee end of bodie s mu st be cente r e d an d at rightangl e s to the ma chined surfac e of cover and mustmove fr e e l y on the float axle .

ASSEMBLY OF COVER TO FUEL BOWL

1. Po sit ion cover abov e fuel bow l and g uide pump int opum p c vlinde r , being c a r eful not to damage floats .

2 . Augn notes in co ve r and ga sket wi th holes in fuel

bowl an d instal l four cover to bowl assembly screws

(77) and lo ckwa shers (76) . Tighten sc r ew s eve nl y

and secure l y .

3 . Instal l fue l union (4), fue l fil te r screen (3). twofiber washe r s (2 and 5) and fuel filte r plug (I ) ,us ing 15/1 6 " wr ench.

zenith carburetor model 29 service manual

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