,,, ..

. , -··t

... _ ,; ,..~

1: ,.

'· Q •

"

I

I ~· ' .1 .

,, . ':· -

I

AID NO. :' 51040 I·

SUBJECT: CARBURETION

.__ -MODEL: '·ALL

i· • I r· I • ..

.·

'.

• < :· .

' \

/ .·. ..... . :.•

. ....... ;. · .. MG .... ... ht

tp://

www.

trium

phwe

dgeo

wner

s.or

g

_,

I N DE X

PREFACE •••

CAR.B URE'IION . . . . . . . TEMPERATURE COMPENSATOR • •

IDLE/SLOW" RUN EMULSION CIRCUITS

CD4 CARBURETOR

BYPASS VALVE OR OVERRUN VALVE

VENT VALVE

MANUAL CHOKE

AUTOMATIC CHOKE (BI-METAL SPRING TYPE)

AUTOMATIC CHOKE O~AX CAPSULE TYPE)

DIAGRAN - CDSEV CARB URETOR RIGHT SIDE

DIAGIVJ1 - CD4 CARBURETOR RIGHT SIDE

DIAGRAM - CD4 CARBURETOR LEFT SIDE

DIAGRAM - CD4T 150 CARBURETOR LEFT SIDE

DIAGRAM - CDSEV CARBURETOR LEFT SIDE

DIAGRAM - CD4VT 175 CARBURETOR LEFI' SIDE

. . .

DIAGMM - CD5T 17 5 CARBURETOR CROSS SECTION •

DIAGRAM - CDSEV CARBURETOR EXPLODED VIEW

DIAGR..t\M - CD4 CARBURETOR EXPLODED VIEW

DIAGRAM - CDFEVX 175 CARBURETOR ••••

DIAGRAM - CDFEVX 175 CARBURETOR EXPLODED VIEW •

DIAGRAM - CD4VT CARBURETOR EXPLODED VIEW

Sl040

i • :;·,, ' .. - .,.... . ........ ----- ":'" . - - ... -·-·

'1 • ..... .:.. .. • .. • - '

...

'

~ . ,

~

1

2

6

7

7

8

9

9

9

12 ·.·.::·]·1.

15 ·:.i)

16

17

18

19

20

21

22

23

24 '

25

26

~ 1 .

i

http

://ww

w.tri

umph

wedg

eown

ers.

org

;

1. I"

I r

.I i I r

.;:J• T •

;.

' ..

1 N DE X (Cont.)

ITEMS THAT MUST NOT BE CHANGED IN SERVICE •

BYPASS VALVE ADJUSTMENT (Where Applicable)

VEN'.! VALVE ADJUSTMENT .

TUNING:

Idle Adjustment . ·. • • • . . . . . . . Fine Mixture Adjustment • • . . . . Mixt~re Needle Adjustment . . . • . Fast Idle Adjustment. (Manual Choke)

AUTOMATIC CHOKE (BI ... METALLIC SPRING 'r'LPE) •

Sl040

Check and Adjust Remove and Refit

~

27

27

28

30 31 31 32

33

33 33

-·----" ·---~ ·: ...... . ............. ·•. ;<:.~:, :!) • . J; . '• r.\', •

http

://ww

w.tri

umph

wedg

eown

ers.

org

::~71 i ,, ?'

.. \

~~ ,. ..

·:·

:·:i ·~ ··I :"•'

:I ':1 r;~

: ; I .,, '' ! .~] .. , : ... . . ·. , ,

,r-: ., ··' l ... .

;:j

','!:

' I ,. .. ~ l! ~- , t} t

·:;1 "·

'1

.'l ...... .. .. ,.

.. !;

· ~ .. l

,I

,, ·.I :.~

':.! I .· .. I

·· . , . ·: ~ ~·l ' I ... ~,

~ ., -~~

' '

..

~

P R E F A C E

The information contained in this booklet is provided as an easy refer-

ence guide For technicians. More detailed information is available in

the appropriate Workshop Manual.

S1040

HIGH ALTITUDE VEHICLES

VEHICLES SOLD IN HIGH ALTITUDE REGIONS MUST HAVE THE CO CHECKED WITH INFRARED EQUIPMENT AND, IF NECESSARY, THE MAIN METERING NEEDLE ADJUSTED TO BRING THE VEHICLE IN SPECIFICA­TION. THE JAGUAR XJ6L AND MGB REQUIRE FIT­MENT OF SPECIAL HIGH ALTITUDE NEEDLE (S) , NEEDLE NUMBERS AND 45M RESPECTIVELY, PRIOR TO THIS ADJUSTMENT. WHEN DESCENDING TO LOW ALTITUDES, THE CO MUST AGAIN BE CHECKED WITH WFRARED EQU IPMENT AND THE MAIN METERING NEEDLE ADJUSTED TO BRING THE VEHICLE INI'O SPECIFICA:.. TION. THE XJ6L AND t-1GB MUST BE REFITTED WITH LOW ALTITUDE NEEDLE(S) BEFORE THE AFOREMENTION-ED ADJUSTMENTS ARE CARRIED OUT. ALL ADJUST-MENrS MUST BE MADE BY MOVING TilE MAIN METERING NEEDLE •

FOR DETAILS ON HOW TO ADJUST CARBURETORS, SEE PAGE 30 OF TH I S TRAINING AID •

THESE INSTRUCTIONS APPLY TO FEDERAL SPECIFICA­TION CARS ONLY.

~ Copyright British Leyland Motors Inc. - 1976

Page 1 of 37

·~j -;:;.'lr -,--- . . -· ....... --·----·-};;r::r_~ :·,,~· . ~'· f '1 • .l • ;l·~ ~~ ~

~ :··

~ ~

·.

http

://ww

w.tri

umph

wedg

eown

ers.

org

·" \ ~;:r~~/

..

51040

CARBURET ION

The Zenith Stromberg carburetor is a constant velocity variable choke

(venturi) carburetor.

The variable choke (Venturi) allo~s an increase or decrease in choke

(v~nturi) size depending upon throttle plate position. This variation

of choke (venturi) size maintains a constant air velocity over the jet

hence allowing a constant depression over the fuel supply at any throttle

plate position.

To achieve a variable choke (venturi), a diaphragm is fitted to a piston

and the pressure above the diaphragm is lowered by the depression created t

in the carburetor low depression area by engine suction hence allo~ing

atmospheric pressure to lift the piston. The underside of the diaphragm

is vented to atm~sphere.

CHOKE (VENTURI)

INTAKE

FUEL SUPPLY

In theory, the diagram above depicts a simple carburetor suitable for

running an engine at a fixed r.p.m. provided some auxiliary method for

starting could provid~ sufficient air velocity to create a depression ~

over the fuel supply to draw out the fuel to m~< with the air. Unfor-

tunately, this si~ple carburetor is unsuitable for automobile use where

a wide range of revs. is desired.

Page 2 of 37

--.- '"' ... -- ---:-:--; .. -- ..

•: ' .. .. , ~ . ,

http

://ww

w.tri

umph

wedg

eown

ers.

org

i ...

!

1 .

!.

I

.j ~ l ' ' I .

'

CHOKE (VENTURI)

FUEL SUPPLY

INTAKE

By controlling t he air velocity by means of a throttle plate, this car-

buretor could run an engine over a very limited r.p.m. range by varying

the air velocity and thereby depression over the fuel supply. While an

improvement, this is still not suitable for automobile use.

CHOKE (VENTURI)

FUEL S ul?l?LY

INTAKE

In addition to controlling the ai r velocity, we now control the choke

(venturi) size which will provide a constant depression over the fuel

supply. However, as the fuel supply rela tive to choke size an~ throttle

plate position is not governed, the carburetor would be r ich at the lower

end and lean at t he higher end a 1 though the r. p. m: range wi 11 be greatly ;:

increased.

Sl040 Page 3 of 37

~-: ~:-- ·--·-... - .. -·- ' . . ( \. ·

~) 1. ~ ..... ...

··'

..,

.. :· ht

tp://

www.

trium

phwe

dgeo

wner

s.or

g

.~

.. . ;·!·

-.

CHOKE (VENTURI).

FUEL SUPPLY

METERING NEEDU:

By addition of a 'stepped tapered' fuel metering needle, the fuel can now

be metered in relationship to the choke (venturi) size and throttle plate

po~ition. This, therefore, gives a basic carburetor with a wide range of

r.p.m. suitable for automobile use.

Piston control is further refined by the addition of a weight/return spring •

In addition, a bridge is built under the piston to create turbulence and

better atomization.

CHOKE (VENTURI) INTAKE

~r----=-;;:..r.f-.METERING

NEEDLE

FUEL SUPPLY

!here is one exception where a constant depression over the jet is net

SlO~O ?nge 4 of 37

- I

" ., ,. '•

.•i.

.. . ,.

http

://ww

w.tri

umph

wedg

eown

ers.

org

rr - .. ·.:-;--·-_. .. )::!. .... ..

desired; this is acceleration. In this case, the throttle would be wide

open and the pis~on should also move to a corresponding position to main---

tain a constant depression of the jet. This, however, would create a too

lean condition for rapid acceleration. Therefore, the piston must be held

down to increase the air velocity over the jet and hence pick up more fuel

necessary under accelerating conditions. This is achieved by a damper

which is a hydraulic device which limit~ initial piston movement to approx•

imately • 070" - .140" depending upon application. The piston then continues

to move up for.cing t he oil in the piston rod co pass on the outside of the .

damper valve. When the throttle is released , the damper valve falls and

allows rapid oil displacement and hence piston return.

Also necessary is a cold starting ~evice normally referred to as a manual

choke. This consists mainly of a disc with a series of small drillings

which, when rotated, allows progressively more drillings to be open to

fuel supply which is dratm into the low depression area of the carburetor.

Federal Law applicable to vehicles produced after 1968 requires further

refinements to control exhaust emissions to closer tolerances at idle

and deceleration, the t~o conditions under wh ich emissions are highest.

SlO.:.O Page 5 of 37

-- ' -- -- -·---·-

., ..

C\ ~

,•

.. http

://ww

w.tri

umph

wedg

eown

ers.

org

,

·~

TEMPERATURE COMPENSATOR

To reduce emissions at idle, a temperature compensator is fitted. This

is a capered valve controlle'd by a temperature sensitive bi-metal strip

designed to allow AIR to bypass the bridge and enter the carburetor in

the low depression area. This weakens t h e depression wh ich t hen allows

the piston to fall slightly thereby cutting available fuel and creating

a leaner mixture.

Sl040 Page 6 of 3i

'I I

..•

http

://ww

w.tri

umph

wedg

eown

ers.

org

..

IDLE/SLOW RUN EMULSION CIRCUITS

INTERNAL- EXTEfu~L VENT VALVE

EMULSION AIR PICK-UP

IDLE AIR REGUlATOR

CD4 CARBURETOR

OWN STREAM DISCHARGE CIRCUIT

The temperature compensator is replaced on some versions of the carbure-

tor by a separate idle/slow speed <;ircuit which discharges mixture down-

stream of the throttle plate - mixture flow, however, is still via the

metering needle.

Also, there is an emulsion circuit for both idle and main fuel feeds

~hich gives improved atomiza tion and a decrease in sensitivity to fuel

viscosity changes due to temperature variations. This system replaces

the temperature compensator on some applications.

St040 Page 7 of 37

'

,. .

~ ~

' ...

'• ;.

http

://ww

w.tri

umph

wedg

eown

ers.

org

OVERRUN VALVE

BYPASS VALVE \

. '

BYPASS VALVE OR OVERRUN VALVE

To control emissions on deceleration either a bypass valve or overrun valve

is fitted. This device allows mixture to bypass the throttle plate to pro-

vide a combustible mixture when the throttle plate is suddenly closed. This

prevents the fuel r e sidue in the intake manifold from passing through the

engine in its raw state. The valve is operated by high manifold vacuum

present in the manifold when the throttle plate is suddenly closed.

<! :

~·~

1 This year all British Leyland models are fitted with Zenith Stromberg car-

~: ,, • 1

buretors with the exception of Jaguar Vl2s. There are, however, variations ,, J '

on model to model application. ~

·,j ., ,.-;- .. /.

•1 .. ~

~ # ., -~

1 Sl040 Page 8 of 3i

~ \ '

.· http

://ww

w.tri

umph

wedg

eown

ers.

org

! I i

I • '

.\

j. • '

j ~

l j

' i . 1 I

VENT VALVE .~ . .. ,r

On some versions there is a vent valve(s) which is operated by throttle

position. Thes~ valves vent the float chambers to the charcoal canister

when at idle· and directly back into the air cleaner hence induction pro-

cess with the throttle open. · It is most important that these valves are

co·rrectly adjusted in order to allow correct function of the anti-run-on

valve, if fitted.

MANUAL CHOKE

Earlier carburetors had a manual choke. The extra fuel necessary to achieve

a cold start is drawn from the float chamber through a series o.f drillings

in a disc and enters the low depression area of the carburetor.

The amount of fuel available_ depends upon the position of the disc which

is controlled by a manually operated cable. Fast idle is achieved by a ... ~ .... ·~::~~~~

fast idle cam and screw.

AtrrDMATIC CHOKE (BI ·METAL SPRING TYPE)

The extra fuel necessary for cold starting is delivered through a jet and

needle assembly to the low depression area of the carburetor. The needle

is connected by a lever on the actuating arm to a temperature sensitive ·

bi-metal spring which is mounted on an aluminum block which forms an en-

gine heated water jacket with the outer cap.

As water temperature increases the bi-metal spring moves the a~tuating arm

in a counterclockwise direction ~o~hich moves the metering needle down, lean-

ing out fuel flow. When the engine is at operating tempera;ure, a sealing

ring on the base of the needle prevents further f ue l flow.

.·

51040 Page 9 of 37

' ·- · ----,.-.,-' ,. · .. ·.. · "\..._~·· .. :· ... . http

://ww

w.tri

umph

wedg

eown

ers.

org

-·

Fast idle is obtained by a stepped cam mounted on the same pivot as the

actuating arm and kept in contact with it by a torsion spring. The

cam operates_a pin which is connected to throttle by a lever. The

steps on the cam give increases in throttle opening proportional to the

position of the bi-metal spring and h~nce fuel enrichment. The pin takes

a position on the cam depending on temperature and throttle opening.

A vacuum kick piston is connected to manifold vacuum by a passage in the

carburetor. Prior to starting, no vacuum exists behind the piston and

the piston return spr.ing, forced by a lever, holds the needle actuating

arm in a clockwise direction thus richening the mixture and opens the

throttle. As soon as the engine is running, vacuum behind the piston

moves the piston down the cylinder. The pist on rod slot disengages from ... the actuating arm and the enrichment is then c ontrol led by the bi·metal-

spr~ng only.

Under hot engine conditions, the bi-metal spring overrides the piston·

spring preventing additional fuel delivery duri~g hot starting.

~ . ... , , • •''

Sl040 Page 10 of 37

.. t .. _, ht

tp://

www.

trium

phwe

dgeo

wner

s.or

g

:·.'Y~,!';·, ·.:.·.: ··\~ · _.;; ... :~.~: ~· .:.~~.,:--~-":..:. .. ·~~:.:.:·~:;.·.._":',._,:...~..: :.: .. ~:;::..:..:._;,._:_-: _ .... -. ......... ~ ·· ,··~...! .. :'\1. '..· ... ~·;.~·.:"':.·:.~ .. ~~.i~.r'~~: ... .:~· ... '·"!- .. 1 t;..;....!~~.;.:,:ti....L~~--:.:_:':.~;: .... ·;:_ . .-.£.'! i· · · ;1 :··-:...c:.....:;_;, -!'-, .. ..!: ~-•-•:;.:..;..--::J.. . -: .~._,.

··~ r, :

j

.. •

.

: '

•

. .. ··· i

! :.'

I

~ :-~ ~~""~ ~~ ~

·~ 5i

Ul ....... 0 .p-0

'"d ll)

()Q fll

....... t-'

0 Ml

w "'-.~

-·

.,

·=~··~ .· . .. ~ . ..... "0 • •

FAST IDLE LEVEJ1.

ACTUATING ARH

STEPPED . CAH

THROTTLE LEVER

!

FAS1' IDLE PIN

I'

VENT VALVE LEVER

DATUM MARK

VACUUM KICK IS TON

'

JET

,j AUTO-CHOKE

.·· u ~>:; -...~.-:

HEAT MASS

f. (

I

WATER jACKET

RETAINING BOLT

j

BI-METAL

I

() \

BI-METAL COIL

. :.~·~ ;,~~~·' ht

tp://

www.

trium

phwe

dgeo

wner

s.or

g

~.

AUTOMATIC CHOKE (WAX CAPSULE TYPE)

The automatic cho~e operates as a small constant depression carburetor.

Increased air and fuel requi rements are governed by a wax capsule which

is sensitive to coolant temperature.

A reduction of coolant temperature opens a throttle valve which increases

the fuel flow proportionally by moving a metering needle which is at tached

to the throttle valve. A depression is maintained in the mixing chamber

by a spring loaded air valve which opens in proportion to air flow. The

throttle valve and metering needl e assembly move within a range at a par-

ticular temperature . The upper limit is the 'start' and the lower limit

the 'run• position .

.. With the engine cranking and the throt t le valve in the 's tart' position,

the depression in the mixing chamber draws fuel into the mixing chamber,

--past ~he throttle valve, and into the engine via the balance passage of

the inlet manifold. As soon as the engine fires, the depression across

the throttle valve is increased which draws the throttle into the 'run'

position.

As the engine warms up , t he wax capsule cl oses the throttle/metering needle

assemb l y until the choke is fully closed and the engine i s running on the

main carburetors.

During acceleration, additional mixture is provided by increasing the load

on the air valve the reby increasing the dep ression in the mixing chamber

~··-... ...

: '

.. I~

'·: 51040 Page 12 of 37 IW

--;-;-· - . ·-.- http

://ww

w.tri

umph

wedg

eown

ers.

org

and hence depression on the jet. This is achieved by a two stage air

valve. The first stage , spring load on the underside of the air valve,

permits the air valve to move proportionally to air. flow. Th~ ~!d~ -~or

the air valve is moveable and the lower end is open to manifold vacuum.

Under high vacuum conditions the guide is drawn into the lower position

against a spring load. Under accelerating conditions, the vacuum is in-

sufficient to act against the spring load and, therefore, moves into the

upper position against the air valve applying additional spring load thereby

increasing the depression in the mixing chamber.

a. Fuel requirements are determined by the profile of the metering

needle.

b . Air flow requirements are determined by the profile of the throttle

plug . .r-~\ ~ .. ~·

-.

Sl040 Page 13 of 3 7

I ~-'7'~· .- - · -····-·--· ·-- ---

~ - http

://ww

w.tri

umph

wedg

eown

ers.

org

':t i I

.! ,,

J I

:1 :, ., '!

.

. -;

I

.:,;

4 '4 .j

~J

·i

:~ ' ., ~

i' 'I

~

-'J -~ ·l -~t I.

·' .J t. .j 4 ··I .;: ., I ~ . ;

' ··" 1 1 ..

. l ·~ .i

•:l . .. i

'•j

·:: ,:• .

I

.. ~ ., '< ;; ' :i \j .. ~

'ij

' ~ i

;·~

<'":")

;.

" ., ' " ·'·

\ -f

~NIFOLD VACUUM CONNECTION

Sl040

THROTTLE VALVE

LINKAGE FROM WAX CAPSULE TO Til.ROTTLE AND .METERnJ'G

NEELDE

FUEL MIXTURE OUTLET

FUEL INLET PASSAGE FROM ~lAIN CARBl!RETOR FT..OAT CH..'\M.BER

WA."\ CAPSULE

Page 14 of 37

WATER JACKET

-.t • . ·'

·~.

.. ·~

.·

., . ··. ' ... .. ... , . ·~

I I.

.. . , http

://ww

w.tri

umph

wedg

eown

ers.

org

] ~ ·:

•·j >?: -.,~ 1

.. j ' I I • i ~ I

. ~ . I

,;'I ·; ~

.. J :;

:_:;_ ~ : . ·:~

I

· .. i

, .. ; ~! · ...... ~

1.(';

{/) ...... 0 ~ 0

"'=' PI

~ ...... VI

0 rt'o

w ......

... a ~

FINE MIXTURE ADJUSTER SCREW

TEMPERATURE COHPENSATOR

.. · ,·; ~: -.. .... _ . .. ...... - . ::~ .....

RIGHT SIDE TEMPERATURE COMPENSATO~

COSEV CARBURETOR

·:~.i)

CRANKCASE AND CHARCOAL CANISTER PURGE PIPE

DECELERATION BY-PASS VALVE

l i ·I

, I. . \

··.J I' ·.· .. ~ ht

tp://

www.

trium

phwe

dgeo

wner

s.or

g

, .. ~ ··~

~-z·~ . ... ._ .l

... ~ .. !

• . ,

'-;

I

... ! ... ,

··: I

~~ : ~ ·. -··-<J ' :1 : • j

~"J ""'\ f.·

··~ :~·

1 ~--. ..

I

I

I

U)

t-' 0 ~ 0

tO Ill

OQ (1)

,_. 0">

0 H't

w -...J

:J

FINE IDLE ADJUSTNENT

.'·~ :.:~-: · ·- .. ;~~-~·:: ::::. ;:: ~

COARSE IDLE ADJUSTMENT

.~. -~~ ..

}•, )

RIGHT STDE/SLOO RUNNING CIRCUIT

CD4 C.ARDURETOR

CRANKCASE AND CHARCOAL CANISTER PURGE PIPE

::)

y "' . .

DECELERATION BY-PASS VALVE

,_ http

://ww

w.tri

umph

wedg

eown

ers.

org

. ~,.}1 ·~~:'~ . ~. -i

. ::.'. j ·. !

•· · •• 1

I I

I ., I !

I ,, ·,

~

/

: • ·' I ~ .

~ ~~. ! •;":' : ? .:..: .t • . ... - : ... ~ ·,

:

~~i ;z1 ~ -~"'!>;;

I

Ul ..... 0 +=-0

~

fL

CHOKE

MAIN MIXTURE ADJUSTMENT

FAST IDLE SCREW

LEFT SIDE MANUAL CHOI@

CD4 CARR\JRF,TOf\ .. ) "~'" . - ~-

EGR CIJr-OUT VALVE

I .,

j

'I

!L .,,, I'

i ··,, I'

h' . -• ., ,,

·---- --

HYDRAULIC DAMPER

. : ~ -:)· , .. ~· ht

tp://

www.

trium

phwe

dgeo

wner

s.or

g

·r · '~-' ~ -~ -

:;__ . ._.,

;.·

' ;

,..

/

., A• . " · . / • I

~!

-• j . ~ i

: .~

I

(Jl ...... ~ 0

"tt I»

(]';I ~

t-' CD

0 Ml

w ......

... - r..- ............. . _

...

I .~.:·:.: .. "·-.. :-: .~--· · = .-':, _:.:; -· .

- .. ·- ~·-- . ~ -~·-·-------.!... .._ __ _,__ ---...--- ~-... --... . . '--"'- --·- .. -·-·· -· . :---:""'--~-'-'-'--·· - -··· ---~-

HA IN MIXTURE ADJUSTMENT

. • ·>

,., . ~· .. • I

....._.··

LEFT SIDE AIJfOMATIC CHOKE

CD4T 150 CARBURETOR - -- --

)

HYDRAlfl.IC DANPER

) - ~· ·:,

http

://ww

w.tri

umph

wedg

eown

ers.

org

·~,..J ;~]( .. "·;

-\~ ; . ~

··:.: ., •

p

' ~

.i ~

;• !

-·~ ~ .i .. ~ 1 .; ·.I

....

{I)

~ 0 f" 0

OQ ~

~ \,£)

0 M\

1..>.1 .......

CHOKE

~ .. ·. ·. . :· . . ;.· ......

LEFT SIDE WlTII VENT VALVE

MAINHIXTURE ADJUSTMENT

IDLE

FAST IDLE SCREW

CDSEV CARBtffiETOR I ,. ,· ~::o::~l \l;t

• • • J~ ·-- •••• -·-· __ .. --L--- - -------

II VENT VALVE' ;·

i; .

HYDRAULIC DAl-tPER

1: '.. L) http

://ww

w.tri

umph

wedg

eown

ers.

org

,.~

~1 • , ";.·,4

~:;l

-.I '-j . [/) ......

.....

~ . )!

,• j f.' :1 ~--~ ·: .{ -, :'' I ~, k~

~

0 ~ 0

'1:1 Ill

OQ It)

N 0

0 ,.., w ~

~ ~ .... ~- "-·· __ .........,.__ ·-·-. -~------ - '----·· ....... ---- -· ..

:.:'-' ·i

LEFT SIDE AUTOMATIC CHOKE AND VENT VNLVE

MAINHIXTURE ADJUSTMENT

VENT VALVE LEVER

THROTTLE STOP AND PICK- UP LEVER

CD4VT 17$ CARBURETOR

'-'·."··~;;· : '"'- .. -_ -:r ~'=' ;.~~ ~:,.;;• • ... . ~- ..... ·.·

VENT VALVE

)

HYDRAULIC DAMPER

. . - . ... .. - -~-! ..

http

://ww

w.tri

umph

wedg

eown

ers.

org

CROSS SECTION SLOW RUNNING CIRCUIT

CDST 175 CARBURETOR

51040 Page 21 of 37

,,

·S")

:, '\ • . .J

,•

· .. '•

,,· '

:.1 http

://ww

w.tri

umph

wedg

eown

ers.

org

, .

-·

I r J I

!

-~

. ·-·

<~ MIXTURE NEEDLE ASSEMBLY

Sl040

EXPLODED VIEi-1 TYPICAL SPECIFICATION TE~PERATURE CO~~ENSATOR

NANUAL CHOKE

:c.'<llli6.F:::.._ T }~ERA T URE C NPENSATOR

FAST IDLE ARM

FAST IDLE

CDSEV CARBURETOR

. (

Page 22 of 37

DIAPHRAGM

NEEDLE RETAIN­ING SCREW

NEEDLE

FLOAT BOWL

: :'~ ~r

·• .. '·•• ,,

·I

http

://ww

w.tri

umph

wedg

eown

ers.

org

MJX!UR:E NEEDLE ASSEMBLY

Sl040

--. .. . . -

EXPLODED VIE't·l TYPICAL SPECIFICAT ION IDLE SLOW RUN CIRCUIT

MANUAL CHOKE

CD4 CARBURETOR

•'

~--SPRING

Page 23 of 37

http

://ww

w.tri

umph

wedg

eown

ers.

org

>~j ·*"' ·1 -~·1 -~'~

~

...

/

~"!' ;. ... . ' . /

.... ~

fj '"' .... r2

..,.

"d I))

()Q (\)

N +=-

0 t-1\

w .......

(I) ....... 0 ~ 0

:· )

ADJUSTING TOOL

...

~0: ::· .. _;.':";·-:;l:.~--:-.?·: ::.:: .;~ :.~s;-. ..::..::-~-_,.:' ~= e:·. ,; · •• ~ ~' •• : .... .._. "': ;• -4:. •

MAIN MIXTUR-E

; .

ADJUSTMENT

IS

WATER INLET & OtrrLET

CDFEVX 175 CARBURETTER

)

DIAPHRAGH

http

://ww

w.tri

umph

wedg

eown

ers.

org

INC NEEDLE FUEL METER

EXPLODED VIEH

. ACTUATL.'JG

AR.L'f

WAX CAPSULE

51040

175 CARBURETOR CDFEVX

,

DAMPER

COVER

CAM BODY

Page 25 of 37

I . ,. •,

. !

http

://ww

w.tri

umph

wedg

eown

ers.

org

.. . ! •' I .· ·, I

·: ::

\• •I

•! · · I

.. ' ~.

~I

I . 1

~. . '

.. - . .... ·.

S1040

MIXTURE NEEDLE ASSEMBLY

EXPLODED VIEW TYPICAL SPECIFICAT ION IDLE SLOt<T RUN CIRC UIT

AUTOMATIC CHOKE

COVER

CD4VT C~RBURETOR

, Page 26 of 37

'\._ ·

. , ': ..

OASHPOT

SPRING

PISTON

.•.

NEEDLE

VENT VALVE

NEEDLE .VAL

FLOAT

nOAT BOWL

1.", . :.;' ...

..... i .. ·:

...... , .,,. :f.

.. .. • ht

tp://

www.

trium

phwe

dgeo

wner

s.or

g

_, I

! . :l ! ..

I

'• .. -.. -~

':

'·

. . .. ·' ,. '.I .,J

'I .I

:I tl

i

i~

j

..

ITEMS THAT MUST NOT BE CHANGED IN SERVICE

1. The jet assembly

2. The pis_ton (air valve)

3. The depression chamber cover

4. the type of Metering Needle (except if instructed for High Altitude

operation)

If any of the above items require changing, the sub-assemblies or the

complete carburetor must be renewed. In the case of the metering needle,

it is permissible to replace the needle providing the procedure for its

installation is carefully followed,

BYPASS VALVE ADJUST~NT (\mERE APPLICABLE)

1. Bring engine to normal operating tempera ture •

2. Remove vacuum pipe from distributor and plug •

3: If bypass valve is floating, the engine speed will r~se abruptly ~o

2000-2500 r.p.m.

4. If the valve is operating correctly, the engine r.p .m . will rise to

1300 r.p.m.

5. *If adjustment is necessary, screw bypass valve clockwise until engine

speed increases abruptly to 2000-2500 r.p.m. or the floating condition.

Turn the screw counterclockwise until the r.p.m. just returns to 1300

r.p.m.

6. Depress throttle and re lease. Engine should drop to approximately

1300 r.p.m. Adjust as necessary to ach.ieve this condition.

* On vehicles equipped with t~in car~ur~tors, before any a~ju5t~~t

51040

can be made, one bypass valve muse ~~ shut off by turni~g th~ ~cjust• ment screw fully counterclockwise.

Page 27 of 37

-. ....,..,. .. --:-""~;::-·· · -~ - ---- ·---- ·- --· '

I

"'

. :.

., •

.. ' . .....

http

://ww

w.tri

umph

wedg

eown

ers.

org

7. Turn the adjuster screw a further half turn counterclockwise. Recon-

nect ~he vacuum pipe.

VENT VALVE ADJUSTMENT

~: It is most important that the vent valve is correctly set on

each carburetor otherwise the operation of the anti-run-on valve

may be affected.

1. Before any adjustment of the vent valves takes place, it is essential

that the engine idle speed is as specified.

2. Stop the engine and remove the existing vent valve tubing from the

carburetor(s).

3. Attach a separate piece of tubing to the vent valve tube on the body

of the carburetor .

4. Blow through th~ tube and at the same time operate the lever operating

the vent valve on ·the side of the carburetor.

5. By operating the l e ver, a sudden restriction can be felt while blowing

down the tube. This will allow the mechanic to 1 feel 1 the valve oper~

S1040 Page 28 of 3i http

://ww

w.tri

umph

wedg

eown

ers.

org

..

ating.

6. Release the·lever and allow the mechanism to return to the condition ....

when at engine idle.

7. Blow through the tube again and if no restriction is apparent, the

vent valve is in a satisfactory position. If, however, a restriction

is felt, turn the adjustment screw counterclockwise until the restric-

tion just disappears. The valve is now correctly set.

51040 Page 29 of 37

. t·.'

., "

lt1A ··: ~ ... ~

' ~ ... ~: • . ..

'/: 'I .. · .. ' .;

:, '>

.. -.. .. ·~ .. -- :~· . ". -~· ·~· ..... ' • ' .. f <.. \" .. ' • • • • -~· . .

.l;.':' • ... "# ... .

http

://ww

w.tri

umph

wedg

eown

ers.

org

j

I.

1 l I I

f '

..

1

~ J J J

Certain v~~icles require that the mixture needle be changed when the vehicle

is operated at ~igh altitude.

PROCEDURE

1. Remove damper and dashpot.

2. Remove air valve complete with diaphragm and mixture needle.

3. Loosen mixture needle fixing screw.

4. Utilizing the mixture needle special adjusting tool, remove the mixture

needle by turning the inner tool counterclockwise. Fit the high alti-

tude needle by turning the inner tool clockwise until the needle shoulder

is flush with air valve base. Tighten lock screw.

S. Reassemble components to carburetor and adjust the mixture by moving the

mixture needle only, until the specified CO reading is obtained.

6. For more detailed instructions on tuning, see the tune-up instructions.

tUNING

IDLE ADJUSTMENT

1. Remove air cleaner.

2. Ensure choke is off and fast idle cam is not in contact with adjustment

screw.

3. Bring engine to normal operating temperature.

4. Disconnect interconnecting links (twin carburetor applications).

5 . Check carburetor a.:r flow is equal. Adjust idle screws as necessary.

6. Tighten interconnecting link • clamp screw. Recheck air flow at each

carburetor.

7. Set idle co specification ensuring equal air flow at each carburetor.

Sl040 Page 30 of 37

-·-.... -- .... ___ ...............

. ~

,. I

·.,

-· .,

.. '

~·

' .. '· . I

:·

' ··

,; ~~

,,-:;· . ' . · .

. :: http

://ww

w.tri

umph

wedg

eown

ers.

org

8. Refit air cleaner.

9. Disconnect air pump outle t hose from pump plug hose. (Do not res trict

pump flow.) ·On MGB, disconnect carburetor vent line;·--

10. Using approved infrared analyser, insert probe into tail pipe as far

as possible.

11.- Check CO reading against that listed on vehicle emission control decal.

FINE MIXTURE ADJUSTMENT

12. If not with specifications, adjust fine mixture adjustment trim screw, ·

(clockwise- richens).

MIXTURE NEEDLE ADJUS'n1ENT

13. If still not within specifications, adj~st mLxture needle with special

tool. (On twin carburetor .applications turn each needle an equal

amount.) - Clockwise to richen, counterclockwise to lean .

14. Top up dampers and hold engine r.p.m. at 2000 r.p.m. for one minute.

15. Recheck CO readings.

~: Do not allow engine to idle for longer than three minutes with-

out clearing out the system by holding throttle at 2000 r.p.m.

for one minute.

All CO readings should be taken from the tail pipe except Jaguar Vl2's

where sampling points are provided in the air injection rails. Also the

Air !njection System must be disconnected whenever CO readings are being

taken.

~t Port of Entry locations, California spec ification vehicles ~ust be ~

checked with the Air Injection System functioning. Dealer testing will

still be performed as described above.

Sl040 Page 31 of 37

. ,

' '

-'

.·

® -.-. ~· ..

'· ' , ',, ,. .. ' ..

http

://ww

w.tri

umph

wedg

eown

ers.

org

.·

' .·

' •

: :r-.. ~·~ . 11 ~: · - ..

:· ..

FAST IDLE ADJUSTMENT (MANUAL CHOKE)

1. Ensure choke cable is correctly adjusted.

2. Pull choke cable out 1/4" to engage fast idle cams in ball locators.

3, Adjust fast idle screws to specification. (Ensure equal air £1~

through each carburetor. twin carburetor applications.)

4. Push choke control c££.

51040 Page 32 of 37

. f .. · ~#flu.

. ..

:, ;, I

..· • f ~~

_;..'

... j l ht

tp://

www.

trium

phwe

dgeo

wner

s.or

g

..

AUTOMATIC CHOKE (BI-METALLIC SPRING TYPE)

CHECK AND ADJUST

~: Prior to removal of a suspect choke unit, the following checks

should be carried out on the vehicle:

1. Check alignment of datum mark on side of heat mass with datum mark

on choke unit body.

· 2. Open throttle and check that head of fast idle pin is flush with

outer edge of guard • .

3. Check.three screws securing choke unit to carburetor Qody for tight-

ness 40 • 45 lb/in.

REMOVE AND REFIT

Removing

1. Remove carburetor(s) from engine.

2. Open throttle and prevent from closing with suitable temporary stop ' (piece of plastic tube or soft wood) in throttle bore •

3. Remove three screws securing choke unit to carburetor body. Remove

choke unit and gasket - discard gasket.

4 . Remove throttle stop screw and locknut.

Sl040 Page 33 of 37

'-f •• : • • ~· .. . : .: , ·e~" .....

~1 . \• .~·. ':·

~ ·. I .'>-;·~

I· ·c. ·~ :• . ...

' . ·~ ...

'i http

://ww

w.tri

umph

wedg

eown

ers.

org

~· : .... .:., ,

\;t

,.

PtAS'IIC TUBE

THROTTLE STOP &NUT

5. Clean face of carburetor to which choke unit is fitted.

6. Remove central bolt, washer, water jacket and sealing ring from choke

unit.

7. Remove three screws and washers securing clamp ring to choke unit· lift

off clamp ring.

8. Carefully remove f~.nned aluminum heat mass ensuring temperature sensi-

tive coil attached is not strained.

9. Remove heat insulator.

S1040 Page 34 of 37

-. ·:; n . --:~- .. # _..... __ ._ . . -· . ....

• •. "l"l.'­

·'··i

·:·.

·' .•

.1.

' ) I

;

··-.. ' ·.•

.,

-~ ..

· ::.·

•. \·,. ·,; ·7' .. ·•· .. . .

I

• ;l! ,, ·' ;~ ' (• .

,: http

://ww

w.tri

umph

wedg

eown

ers.

org

) •I I

"

INSULATOR

BOLT

HEAT MASS WATER JACKET WASHER

Refitting

10. Fit new gasket to carburetor. Do not use sealing compound.

11. Fit choke unit to carburetor tightening the three screws progressively

and evenly to a torque of 40 - 45 lb/in.

12! Fit throttle stop screw and locknut.

13 . Check clearance beeween fast idle pin and base circle of cam is as

. ' follows:

Open throttle and remove temporary stop. Allow throttle to close nor~

mally. Screw down idle speed screw until the clearance between the

lugs is 0.10 in. minimum. Lightly rotate thermostat lever with finger

in an anticlockwise direction to the fully 'off' position.

14. If necessary, adjust throttle stop screw until correct clearance is

obtained. Using the nut, lock the throttle stop screw securely and

recheck the clea;.:ance as detailed above.

15. Replace heat insulator with thermostat arm protruding through slot

provided.

Sl040 Page 35 of 37

~~~:!! f ....... .. ..

: .. ~·

.· •.

·.· ....

· ,· ,. ,·i

'·

• ~ l

'· . )" .. http

://ww

w.tri

umph

wedg

eown

ers.

org

,·

,,-

.-._, .;· ... : ,

16. Replace finned aluminum heat mass ensuring proper engagement of

thermostat arm with rectangular loop of temperature sensitive coil.

To check engagement, rotate heat mass 30° to 40° only in both direc-

tiona. In each case the unit should spring back to its original posi-

tion.

CAUTION: On no account should the hea t mass be rotated more than 30°

THRarTLE SCREW

LOCK NUI

51040

to 40° as the coil could be permanently damaged.

__! 0·10in . t (2·5mm) minimum

Page 36 of 37 :·r·T ;:7: ; · • ... : .. - , -:- .. ---. - ••

I • o.' -14 f

·- - , .. - -.,-... ··-.~-r ,..·.~--- ... ----·· http

://ww

w.tri

umph

wedg

eown

ers.

org

)

I ':

' . . '

l t· I t,

l I . ;:

I

I r

I .

... ,. •

I j I I

' ~ ( 't '

l ,. t t. I r r .

t-· .

~ .. f~~, .. '1•- ~ ' ,,

;

17. Replace clamp ring and three screws and washers. Do not tighten.

18. Rotate heat mass in anticlockwise direction until index mark on

outer edge is aligned with datum mark on body of choke unit.

19. Hold heat mass with index mark correctly aligned and tighten three

20.

21.

22. '

screws securing clamp plate to a torque of 8 - 10 lb/in.

Replace sealing ring and wat~r jacket ensuring that water pipe con­

nections are correctly positioned.

Replace central bolt and aluminum washer and tighten to a torque of

65 - 75 lb/1n.

Reset idle speed screw. , .

23. Repeat on other carburetor if fitted.

24. Refit carburetor(s ) t o engine as detailed in Workshop Manual.

;,..

t •:

• , '? 0 ~~ ...

··~

. .. '

r .. '·

i·

.. 0 <'•

·-:' ··'

I

.~

• .

o I ... ,.

. :

.. . . .,

. • f ..... )

Sl040 Page 37 of 37 ~ I •

-----··---- -·-· -· · ....----- ---· ... --~-;··: ~-."::or. -:;~;:·,:" -;-:._--r--~ ··: ~':\'!~ http

://ww

w.tri

umph

wedg

eown

ers.

org