lift FIAT 500 1972 1.G Workshop Manual

The interior of the car can be heated by the engine
warmed air being ducted into the front compartment and
controlled by a lever on the heating system tunnel.
Engine ignition is by a battery, ignition coil and distribu-
tor which is driven by a gear on the camshaft. The engine
is started by an electric starter motor which is mounted on
the gearbox casing and is controlled by a lever located
behind the gearchange lever.
The complete power unit is mounted by a spring support
at the centre of the rear b o d y crossmember and by t w o
rubber pads mounted laterally to the gearbox.
1 :2 Engine removal (sedan—all versions)
To remove the engine from the car proceed as follows:
Raise t h e rear of t h e car and place on firmly based
stands placed under suitable brackets on the underside
of the body.
Disconnect the battery positive terminal clamp from the
battery terminal post. Release the clip securing the main
petrol pipe to the tank sender unit and ease t h e pipe
from the unit. Drain the oil from the engine sump into
a suitably sized container.
D i s c o n n e c t t h e rear number plate light wire (see
FIG 1 : 6) . Release t h e engine compartment lid check
strap from its slot and separate the lid from the body by
sliding the hinge apart.
Remove the cables attached to the ignition coil, also
to the generator and the starter motor. Remove the
starter motor control tie rod.
Release the oil pressure
indicator cable, the main petrol pipeline at the pump,
the accelerator and starting device controls.
Remove the t w o hoses of the heating and cooling
system which are the input hose to the blower and the
hose for the car heating system. Release and lift out the
engine apron. Remove the starter motor mounting bolts
and carefully lift away the motor.
Using a garage hydraulic jack with suitable cradle (see
FIG 1 : 7) or a rope sling relieve the engine weight
from its mountings. Remove the nuts securing the
gearbox to the engine and the flywheel protection
apron.
Remove the bolts fixing the elastic support to the cross-
member. Remove the rear crossmember mounting nuts
noting that the engine earth cable is held by one
mounting nut and lift away the crossmember.
Carefully ease t h e engine away from the gearbox
ensuring that there is no strain placed on the clutch
shaft. Lower the engine to the floor taking care that no
weight is allowed on any of the attachments. 1
2
3
4
5
6
7
8
1 :3 Engine removal (station wagon)
To remove the engine from the station wagon proceed
as follows:
1 Raise t h e rear of the vehicle and place on firmly based
stands placed under suitable brackets on the underside
of the body.
2 Disconnect the battery positive terminal clamp from
the battery terminal post. Release the clip securing the
main petrol pipe to the tank sender unit and ease the
pipe from the unit. Drain the oil from the engine sump
into a clean dry container of suitable size.
3 H o l d t h e rear door open and secure using string to stop
it swinging to the closed position. Secure the luggage
compartment floor panel in its upright position.
F50013 4 Remove the cables attached to the ignition coil, also
to the generator and starter motor. Remove the starter
motor control tie rod. Release the o i l pressure indicator
cable, the main petrol pipeline at the pump, the accele-
rator and starting device controls. Disconnect the air
filter housing.
5 Remove the hose connecting the car heating system
to the engine cowling. Disconnect the clip holding the
air pipe to the blower and carefully disconnect the pipe
from the blower cowling. Remove the starter motor
mounting bolts and carefully lift away the motor. FIG 1:5 120.000 engine assembly: cross-section view
through a cylinder

LID CHECK A R M
FIG 1:6 Engine compartment lid open LID LOCKING
HOOK
NUMBER PLATE
LAMP CABLE NUMBER PLATE LAMP
CABLE JUNCTION
CROSS MEMBER ARR.2O74.
FIG 1 :7 Engine removal using the jack with cross-
member Arr.2074
6 Using a garage hydraulic jack with a suitable cradle
relieve the engine weight from its mountings. Remove
the nuts securing the gearbox to the engine.
7 Remove the nuts securing the rear bumper blade and
panel to the body. Note that the engine earth cable is
held by one mounting nut. Carefully dismantle the
engine elastic mounting or release the bracket from the
engine rear cover by removing the two nuts and washers.
Lift away t h e rear panel assembly carefully making sure
14
FIG 1 : 8 Engine components: crankcase, cylinder head,
timing sprockets cover To dismantle the engine proceed as follows:
1 Remove the exhaust silencer by releasing the two
collars for attachment to the engine and the two con-
nections for the exhaust pipe. It will be noted that
there is one exhaust pipe connection on either side
of the cylinder head.
2 Place the engine on a firm wooden top bench. Remove
the two tappet cover retaining nuts and washers and
lift away the cover. Remove the connection for cooling
air delivery to the sump cooling ducts at the side of
the sump.
3 Remove the air cleaner after first releasing the two
bolts on the air cowling and the two nuts for the air
elbow connection to the carburetter.
4 Remove the generator drive belt by releasing the
three nuts so splitting the semi-pulley. Lift away the
drive belt.
5 Remove all the bolts securing the air conveyor
ducting to the cylinder head, to the crankcase and
also to the engine cowling assembly opposite to the
air conveyor. Release the accelerator control tie rod
and carefully lift away the air conveyor assembly
complete with the generator after first removing the
clamp fixing the generator to the crankcase. 1 :4 Engine disassembly (sedan—all versions) t h a t rear air ducting panels are not strained or the
mating faces damaged.
8 Carefully ease the engine away from the gearbox ensur-
ing that there is no strain placed on the clutch shaft.
Lower the engine to the floor taking care that no weight
is allowed on any of the attachments.

6 Release the ignition distributor support retaining nut
and lift away the distributor together w i t h its support.
7 Remove all the mounting bolts of the engine cooling
cowling and lift away the assembly. Release the t w o
carburetter retaining nuts and carefully remove the
carburetter together with its drip tray.
8 Lift away the valve rocker assembly having first
released the t w o retaining nuts together with the plain
washers and lock washers. Carefully lift out the valve
rocker pushrods noting their relevant positions.
9 Slacken the four central cylinder head cap nuts and
the four conventional nuts in the order, shown in
FIG 1 :44 or 1 :46. Lift the cylinder head from the
barrels. If difficulty is experienced it is essential to use
Fiat tool A.40014 or a similar drilled plate, otherwise
serious damage could be caused if other means are
used (see FIG 1:9).
10 Remove the four pushrod sleeves and the casing
containing the oil ducting to the overhead valve gear.
11 Remove the fuel pump retaining nuts and washers
and lift away the pump. Carefully pull out the pump
control pushrod from the crankcase.
12 Remove the six screws holding the centrifugal oil filter
pulley cover and lift away the cover. Remove the
centrifugal filter mounting flange by unscrewing the
crankshaft central bolt. Also remove the timing cover
containing the oil pump gears and the oil pressure
regulating valve. Note the position of the nuts,
toothed and plain
washers for correct reassembly.
13 Release t h e four camshaft sprocket retaining bolts and
lift away the sprocket and timing chain. Using Fiat
pulley A.46020 or a large universal two-leg puller as
shown in FIG 1 :10 remove the crankshaft sprocket
and its body.
14 Carefully lift out the rocker pushrod tappets making a
note of their location and gently pull out the camshaft
making sure the front bearing bore is not damaged by
the cam lobes or distributor drive gear.
15 Mark the flywheel and crankshaft to ensure correct
reassembly and release the six f l y w h e e l retaining bolts
together w i t h the lockwashers and lift away the fly-
wheel.
16 Using Fiat tool A.60156 on the two central studs, lock
the two cylinder barrels in place as shown in FIG 1 : 1 1.
TOOL A. 40014
FIG 1:9 Tool A.40014 for cylinder head removal
F50015
17 Turn the engine upside down ensuring that no weight
is placed on the studs and remove the oil sump and the
oil suction scoop.
18 Mark the connecting rods and end caps to ensure
correct reassembly and remove the end caps. Place the
engine on its side and remove the cylinder barrels
clamp. Ensure that the studs are clean and carefully
slide off the connecting rod-piston-cylinder assem-
blies from the crankcase.
19 Remove the six screws holding the rear main bearing
housing to the crankcase and lift away the housing.
Remove the six screws holding the front main bearing
housing to the crankcase and lift away the housing.
20 Carefully ease the crankshaft from the crankcase
moving it diagonally to assist withdrawal. FIG 1:11 Cylinder hold-down tool A.601 56 TOOL A.60156 FIG 1 :10 Removing crankshaft sprocket w i t h puller
A.46020
PULLER A.46020

STUD REMOVAL
PULLER 40010
FIG 1 :12 Removal of stud from crankcase by puller
A.40010
FIG 1 :13 Engine without blower cowling and cylinder
head cover.SPACER A N D CONNECTION
FOR ROCKER SHAFT
LUBRICATION TUBE
OILVAPOR
.VENT PIPE
CASINGS FOR PUSHRODS
(AND OIL RETURN
TO CRANKCASE
21 To ensure no damage occurs to the long cylinder
barrel mounting studs these may be removed using
Fiat puller A.40010 or a universal stud removal as
shown in FIG 1 :12.
1 :5 Engine disassembly (station wagon)
To dismantle the engine proceed as follows:
1 Remove the exhaust silencer and manifold by releasing
the four nuts holding the two flanges from the cylinder
head. Also disconnect the two silencer mounting
brackets and lift away the exhaust system (see
FIG 1 : 2).
2 Place the engine on a firm wooden top bench. Release
the clip holding the tappet cover and lift away together
with the drip tray. Disconnect the fuel line and throttle
linkage at the carburetter and carefully lift away the
carburetter together with its insulator joint and gaskets.
3 Remove the generator drive belt by releasing the three
nuts so splitting the semi-pulley. Lift away the drive
belt.
16
FIG 1 :14 Tool A.60084 for valve and valve springremoval
TOOL A . 60084
4 Remove all the bolts securing the air conveyor ducting
to the cylinder head and to the crankcase, carefully
separate the panels and lift away the separate panels
ensuring no damage is caused to the mating faces.
5 Release the ignition distributor retaining bolt and lift
away the distributor.
6 Remove the fuel pump retaining bolts and also the
three fuel pipe retaining clips and lift away the fuel
pump assembly together with the insulator, gaskets
and control rod.
7 Release the t w o valve rocker retaining nuts, note the
order of assembly of washers and ease away the rocker
shaft assembly from the top of the cylinder head.
Carefully lift out the valve rocker pushrods noting
their relevent positions for correct reassembly.
8 Slacken the four cylinder head cap nuts and the four
conventional nuts in the order shown in FIG 1 :46. Lift
the cylinder head away from the barrels. If difficulty is
experienced it is essential to use Fiat tool A.40014 or a
similar drilled plate as shown in FIG 1 :9, otherwise
serious damage could be caused if other means are
used.
9 Remove the four pushrod sleeves and the casing con-
taining the oil ducting to the overhead valve gear.
10 Remove the six screws holding the centrifugal oil filter
pulley cover and lift away the cover. Remove the
centrifugal filter mounting flange by unscrewing the
crankshaft central bolt. Also remove the timing cover
f r o m t h e rear of t h e crankcase. Note carefully the posi-
tion of the nuts, toothed and plain washers for correct
reassembly.
11 Release the four camshaft sprocket retaining bolts
and lift away the sprocket and timing chain. Using
Fiat puller A.46020 or a large universal two-leg puller
as shown in FIG 1 : 1 0 remove the crankshaft
sprocket and its key
12 Carefully lift out the rocker pushrod tappets making a
note of their location and gently pull out the camshaft
making sure that the front bearing bore is not
damaged by the cam lobes.

13 Remove all the bolts and washers joining the sump
casting to the crankcase making a special note of the
location of bolts of different lengths.
14 Mark the flywheel and crankshaft to ensure correct
reassembly and release the six flywheel retaining bolts
together with the lockwashers and lift away the fly-
wheel.
15 Using Fiat tool A.60156 on the two central studs, lock
the t w o cylinder barrels in place (see FIG 1 :11).
16 Turn the engine upside down ensuring that no weight
is placed on the studs.
17 Mark the connecting rods and end caps to ensure cor-
rect reassembly and remove the end caps. Place the
engine on its side and remove the cylinder barrels
clamp. Ensure t h a t t h e studs are clean and carefully
slide off the connecting rod-piston-cylinder assem-
blies from the crankcase.
18 Remove the six screws holding the rear bearing hous-
ing to the crankcase and lift away the housing. Remove
the six screws holding the front main bearing housing
to the crankcase and lift away its housing.
19 Carefully ease t h e crankshaft from the crankcase
moving it diagonally to assist w i t h d r a w a l .
20 To ensure no damage occurs to the long cylinder
barrel mounting studs these may be removed using
Fiat puller A.40010 or a universal stud remover as
shown in FIG 1 :12.
1 :6 Cylinder head removal, servicing and replace-
ment
Description:
The aluminium cylinder head is finned to increase the
cooling surface. Through bolts secure the head and the
two cylinders to the crankcase. The valves are controlled
by a camshaft through tappets, pushrods and rockers. The
connection between the head and the crankcase is via five
sleeves mounted directly between the head and crankcase,
and these accommodate the pushrods, lubricating oil and
passage for the crankcase gases. The cylinder head has
been
modified for the 110 F and later 120 engines as
they now incorporate a heater safety device as described
in Section 4 : 4 .
FIG 1:15 Cylinder head
17F500
The cylinder head should be removed whenever the
valves require attention or the engine to be decarbonized.
To remove the cylinder head proceed as f o l l o w s :
1 Remove the air cleaner, carburetter, rocker cover and the
screws securing the blower conveyor to the cylinder Removal of cylinder head: FIG 1 :17 Installing a valve guide using Tool A.60153
provided with pilot bush TOOL A. 6 0 1 5 3 -
WITH PILOT BUSH FIG 1:16 Cleaning valve guides
W I R E BRUSH A.11417 / BIS

INTAKEEXHAUSTINTAKEEXHAUST
FIG 1 :18 Main specifications of intake and exhaust valves and valves guides (dimensions in mm)
head. Disconnect the t w o side exhaust manifolds.
Note the spark plug HT cables locations and dis-
connect from spark plugs.
2 Remove the rocker shaft pedestal- and lift away the
rocker gear. Extract the pushrods, making a careful
note of their location. Remove the cylinder head hold
down nuts in the order shown in FIG 1 :44 and using a
puller as shown in FIG 1 :9 lift off the head.
Dismantling the cylinder head:
1 Using Fiat valve spring compressor A.60084 or a uni-
versal spring compressor depress the valve spring as
shown in FIG 1 :14 and lift out the cotters. Release t h e
compressor and withdraw the lock cone, oil shield
(inlet valve only) upper spring cup, valve spring and
lower spring cup. Withdraw the valve from the under-
side of the head.
2 Dismantle the remaining three valve assemblies as
detailed above ensuring that all parts are kept in sets
for correct reassembly.
Inspection and servicing of the cylinder head :
1 Remove all carbon deposits from the combustion
chambers and valve ports using a rotary wire brush or a
set of scrapers.
2 Thoroughly clean the cylinder head and to test for dis-
tortion lightly coat the machined faces with 'Engineers
Blue' or lamp
black and place the cylinder head on a
surface plate. Carefully slide to and fro and any streaks
left behind will indicate a distorted surface. A distorted
head will not make a gas-tight seal with the cylinders
and must be entrusted to an expert for correction or,
in severe cases, renewed.
3 Carefully clean the valve guides as shown in FIG 1:16
using Fiat guide brush A.11417 bis. Should the guides
18Reassembly is the reverse procedure to dismantling.
During assembly utmost cleanliness must be observed as
any abrasive material could find its way to the pistons and
cylinder bores causing unnecessary wear. Check that the
cylinder barrel mating face is clean to ensure correct
gasket sealing.Reassembly of t h e cylinder head:
be worn then they should be removed using a press and
a suitable sized drift. The guides are press fitted with a
pinch fit of .00134 to .00244 inch. To install the guides
use Fiat tool A.601 53 as shown in FIG 1 :17. As the
guides have no stop ring during the press fitting, the
depth of insertion is determined by the Fiat tool. If the
tool is not available take the necessary depth measure-
ments before the old guides are removed. The normal
fit clearance between valve stem and guide is .00087 to
.00217 inch with a maximum wear limit of .0059 inch.
To check this see FIG 1:18.
4 The valve seats should always be reconditioned after
decarbonization. It is suggested that this operation be
left to a local service station with valve seat cutting
equipment. The valve seat angle for both inlet and
exhaust valves is 4 5 ° ± 5'.
5 Inspect the valves for soundness or distortion and if the
clearance between guide and stem is within the manu-
facturers wear tolerance of .0049 inch the valve may
be cleaned using a wire brush and the seating face
ground to an angle of 45°30' ± 5'. This again should
be left to the local service station.
Valve springs:
Thoroughly clean the valve springs of oil deposit and
inspect for cracks. It is advisable to check the free spring
height and if this dimension differs from the original
height, details of which are given in Technical Data, the
spring must be renewed. Any decrease in length indicates
that the spring has weakened.

After the crankshaft has been reground it is important
that all traces of swarf are removed by constant washing
and then drying with a non-fluffy rag.
The clearance between the main bearings and journals
must be checked before installing the crankshaft in the
engine. It should also serve as a recheck after the
crankshaft has been reground.
Measure the maximum main bearing internal
diameter and the minimum journal diameter using
accurate measuring equipment. The clearance must not
exceed .0039 inch otherwise the journals must be
reground and undersize bearings fitted.
Undersize bearings w i t h .0394 inch stock on the
internal diameter are also supplied unmounted. They
must be press fitted in the supports, the recommended
interference fit being .00039 to .00197 inch. After
pressing the bearing into the support, a hole is drilled in
the bearing in line with the location dowel hole in the
support. The hole is finished with a suitable expanding
reamer, such as Fiat U.0334, and the dowel pressed i n ,
noting that the hollow dowel fits in the flywheel end
support.
The next stage is to heat the assembly in an oven or
oil bath for a period of one hour at 150°C (302°F).
When the assembly has cooled to room temperature,
the bearing is reamed in a lathe to match the crankshaft
journal size.
3
Crankshaft oil seals:
Two inner spring rubber oil seals are located, one in a
special seat in the timing gear cover and the other in the
flywheel end of the crankshaft support and provide oil
tightness. These seals are shown in FIGS 1 :3 and 1 :34.
Whenever the engine is dismantled for overhaul these
seals should be carefully inspected for correct seating and
that the inner seal surface is not worn and that the contact
area is perfect both on the crankshaft and on the fan and
generator drive pulley hub.
Clutch shaft pilot bushing:
A self-lubricating bronze bush is fitted in the end of the
crankshaft as shown in FIG 1 :34 and provides a bearing
for the clutch shaft. Should the bush be worn use Fiat
puller A.40006/1 /2 to remove the worn bush. A new bush
should be fitted using a suitably sized drift.
1:12 Flywheel and starter ring gear
The flywheel should be inspected for wear at the clutch
driven plate contact area. It should be flat and have a
smooth finish.
The ring gear teeth should be cheeked for damage
which if evident, the ring gear must be replaced. To facili-
tate the fitting of a new ring gear on the flywheel, the new
ring gear should be heated in an oil bath to a temperature
of 80°C (176°F). Using a press gently ease the
expanded
ring gear over the flywheel and press fully home.
1:13 The oil pump
Sedan :
A helical-spur gear type oil pump is driven by the cam-
shaft through a front dog drive coupling. The gears are
F50025 To remove the pump from the engine proceed as
follows:Pump removal and reassembly:
Remove the engine rear central support from the timing
gear casing. Remove the filter cover pulley and lift
away the drive belt.
Release the hollow screw attaching the slinger and the
mounting flange of the filter on the crankshaft. Also
release the nuts fixing the timing gear cover to the
crankcase.
Remove the timing gear cover together with the oil
pump assembly and the pressure relief valve.
Lift out the oil pump suction scoop with the filter
screen attached from the sump.
Reassembly of the pump to the engine is the reverse
procedure to dismantling. 1
2
3
4
5 located in a special housing in the timing gear cover and
held in place by a cover plate. The oil pressure relief valve
is mounted on the drive gear shaft guide.
A pump suction scoop fitted with a filter screen is
secured in the crankcase and connects to a duct in the
timing gear case as s h o w n in FIG 1 :36.
2
4
6Key t o Fig 1 :36
Rocker shaft
Ducts, cylinder head oil drain
Oil pressure relief valve
to centrifugal filter
9
with central oil gallery
12Sump cooling air conveyor
indicator sending unitOil filler with vent valve
Line, oil delivery to rocker shaft
Level indicator rod 31
5
7Gear pump
8 Oil duct
Centrifugal oil fitter
1110
Crankshaft
Oil pump intake screen filter
13 Low oil pressure FIG 1:36 Engine lubrication diagram

CHAPTER 2
THE FUEL SYSTEM
2:1 Description
2 : 2 Fuel pump operating principles
2 : 3 Routine maintenance
2 : 4 Pump removal, dismantling and examination
2 : 5 Reassembly, installation and adjustment
2 : 6 Carburetter operation and adjustment,
Weber 26.1MB2 : 7 Modifications
2 : 8 Carburetter operation and adjustment,
Weber 26.OC
2 :9 Air cleaner
2 : 1 0 B l o w - b y gases recirculation device
2:11 Fuel tank
2:12 Fault diagnosis
2:1 Description
All the new 500 models use a mechanical diaphragm
fuel feed pump as shown in FIG 2 : 1. Four types of
carburetter are fitted depending on the model to which
the engine is installed. Each carburetter operation and
adjustment is fully described, together with details of the
recirculation device for blow-by gases and o i l vapours.
2 : 2 Fuel pump operating principles
Refer to FIG 2 : 2. An eccentric on the rotating camshaft
actuates the operating rocker 21 via a pushrod 25 which
depresses the diaphragm 14 and so creates a depression
in the pumping chamber located in upper body 5. Under
atmospheric pressure, petrol passes through the pipeline
connection and inlet valve into the pumping chamber.
The return spring 15 then raises the diaphragm, expelling
the petrol through the outlet valve and pipeline to the
carburetter float chamber.
When the float chamber is full, the pressure in the pipe-
line and pumping chamber holds the diaphragm depressed
against the tension of the return spring.2 : 3 Routine maintenance
A poor delivery of fuel to the carburetter may be due to
a fault in the fuel pump or related lines. Periodically the
pump body screws 19 (see FIG 2 : 2) and upper cover
screw 1 should be checked for tightness. The fuel pump
lines should be disconnected and checked for freedom of
restriction, chafing and loose connections. The fuel pump
filter should be removed and cleaned periodically.
2:4 Pump removal, dismantling and examination
The pump is located on the carburetter side of the
engine crankcase (sedan) or under the generator at the
front of the crankcase (station wagon).
Removal:
1 Disconnect the fuel pipe from the tank to stop petrol
syphoning out of the tank and then release the fuel
inlet and outlet pipes from the pump body.
2 Remove the t w o nuts and washers holding pump to
crankcase.
3 Carefully lift away the pump, gaskets and insulating pad
from the crankcase (see FIG 2 : 3).
F50035

CONTROL ROCKER FROM TANK TO CARBURETOR
FIG 2 : 1 Fuel pump. Arrows point to fuel inlet and outlet
FIG 2 : 2 Fuel pump components
KeytoFig2:2 1 Cover screw 2 Screw gasket3 Cover gasket 4 Cover 5 Upper body
6 Spring for inlet valve 7 Inlet valve 8 Outlet valve
9 Spring for outlet valve 10 Plate gasket 11 Plate screws
12 Valve retaining plate 13 Filter gauze 14 Diaphragm,
complete with tie rod 15 Return spring 16 Spring
thrust cup 17 Felt 18 Washer for felt
1 9 Connection screws 20 Lower body 21 Rocker
22, 24 Gaskets 23 Insulating pad 25 Pump control
pushrod
36
FIG 2 : 3 Fuel pump and control pushrod
FUELPUMP CONTROLPUSHROD
INSULATING
PAD
FUEL PUMP
A l l 500 Sedans are equipped with Weber type 26. IMB
carburetters w i t h detail differences only between the
models. The carburetter is of a downdraft single choke 2 : 6 Carburetter operation and adjustment,
Weber 26.IMB Carefully slide the pump control pushrod into the
crankcase, assemble the t w o gaskets w i t h the insulating
pad in between and slide over the pump retaining studs.
Ease t h e p u m p towards the crankcase ensuring the push-
rod locates correctly in the rocker end. Finally tighten the
two retaining nuts and spring washers. Installation:Ensure t h a t all parts are clean and dry. Assembling is the
reverse procedure of dismantling. Lubricate the rocker
lever and pin before placing them in the lower body. 2 : 5 Reassembly, installation and adjustment 1 Refer to FIG 2 : 2 and remove the cover mounting
screw 1 and washer 2. Lift off cover 4 and filter 13.
Mark the relative position of the two halves of the pump
body. Remove the pump bodies interlocking screws 19
and separate the upper half from the lower half of the
body.
2 Push down the centre of the diaphragm assembly 14
and rotate through 90 deg. to release diaphragm from
the rocker 2 1 . Lift out diaphragm and spring 15.
3 Release the t w o valve assemblies in the upper body by
removing the valve retaining plate locking screws 1 1 ,
and lifting out the plate 12, gasket 10, valve springs 6
and 9, and valves 7 and 8.
4 Using a pin punch remove the rocker pivot pin together
w i t h the t w o washers and carefully lift away rocker and
reaction spring.
5 Thoroughly wash all components in petrol and
blow
dry with compressed air or a foot pump. Inspect the
valves 7 and 8 for evidence of damage and valve springs
6 and 9 for weakness or cracks. Check to see that the
diaphragm reaction spring and rocker are not distorted
or unserviceable. Generally inspect all parts for cracks,
distortion and the diaphragm for stiffness and also the
rocker and pin for wear. Dismantling:

FIG 2 : 6 Weber 26.IMB carburetter starting device
(choke) end
Key to Fig 2 : 6 1 Choke device cover 2 Bowden
mounting screw 3 Nut and screw, choke bowden wire
4 Choke control lever A Position of lever 4 for 'fully
inserted' choke B 'Partially inserted' choke
C 'Disinserted' choke
caused by the engine suction and the charge is then drawn
into the cylinders.
The secondary venturi 24 is to increase the vacuum
around the nozzle 25 and to carry the charge to the centre
of the primary venturi 2 1 .
When the engine is idling, fuel is carried from the well
23 via an appropriate passage to the idle speed jet 13
where it is mixed with the air coming from the air inlet 5.
Through duct 3 and idle speed orifice 18 (adjustable by
means of a taper point screw 17), the fuel reaches the
carburetter throat, past throttle butterfly 19 where it is
further mixed with the air stream drawn in by the engine
vacuum through the gap around the throttle in the idling
speed position.
From the d u c t 3 the mixture can also reach the car-
buretter throttle chamber through a transition hole 20
which is located in exact relation to the throttle butterfly.
The purpose of this progression hole is to permit a smooth
acceleration of the engine from the idling speed, this being
proportional to the increase in the throttle opening.
Starting device:
This enables the engine to be started when it is cold
under the most arduous of weather conditions. It is con-
trolled by means of a lever placed behind the gearshift
lever and must be progressively adjusted to its normal
rest
position as the engine reaches the normal operating tem-
perature. The starting device comprises a valve 33 (see
FIG 2 : 5) actuated by the lug of the rocker 36 which is
connected to the control lever 38 by a suitable shaft. By
38
pulling the device control fully across through lever 38
and rocker 36, the valve 33 is lifted from its seating and
brought into the 'fully open' position. Refer to diagram 'A'
(FIG 2 : 5) . Under these conditions the valve 33 closes
the air hole 27 and the mixture hole 29 and uncovers
mixture orifices 30 and 32 which also communicate with
the starting jet 46 through a duct 26 and air holes 35.
With the valve 33 partially open the hole 29 may com-
municate with the carburetter throat through the valve
central slot, duct 28 and the hole 31 drilled in the venturi
21 corresponding with the venturi restriction.
When the throttle is set at the idling speed position, the
engine vacuum caused by the operation of the starter
enables the fuel contained in the recess of jet 4 6 , in the jet
and in the reserve well 45 to be mixed w i t h the air coming
from holes 43 and 44. The mixture arrives through the duct
26 and holes 30 and 32, at the same time as air passing
from the holes 35, past the throttle through duct 34 so
permitting easy starting of the engine.
After the engine has fired initially, the device will deliver
a charge with a rich petrol/air ratio so as to permit regular
running of the engine whilst it is cold. As soon as the
engine has warmed up to normal operating temperature
this charge would obviously be too rich and therefore it is
necessary to gradually ease o f f the operation of the starting
device as the engine reaches its normal operating tempera-
ture. During this adjustment the valve 43 slowly uncovers
the hole 27 which will permit a greater amount of air to
enter through the spring guide hole 42 so weakening the
mixture at the same time as closing the progression holes
30 and 32 and air holes 35 the amount of mixture is also
reduced. See diagram ' B ' (FIG 2 : 5).
The hole 29, the duct 28 and the hole 3 1 , which are
drilled in the venturi 21 permit a regular progression of
acceleration whilst the engine is cold as well as when it is
at normal operating temperature. By opening the throttle
butterfly 19 to increase the speed of the engine the
vacuum acting on the duct 34 is decreased. This causes a
drop in the amount of fuel delivered through duct 34 with
consequent irregular running of the engine but, through
hole 3 1 , duct 28 and hole 29 some charge is sucked in by
the vacuum formed in the restriction of the venturi, caused
by the opening of the throttle and this automatically com-
pensates for the reduction in the delivery through the duct
34.
When the starting device is not in operation, valve 33
covers the hole 29 and so preventing the passing of fresh
charge. Diagram ' C (FIG 2:5).
Engine s t a rting:
So that full advantage may be taken of the progressive
action starting device the engine should be started as
follows:
1 Cold starts:
The starting device should be moved across the position
'A', (FIG 2 : 6) . Once the engine has fired push the control
in partially.
2 Warm starts:
Only partially move the starting device as shown in
position 'B' (FIG 2 : 6).