Carburetter Operation And Adjustment, Weber 26. Oc; Carburetter Operation, Starting Device:; Section Of Later Starting Device - Fiat 500L Workshop Manual

FIG 2:12 illustrates the starting device fitted to
26.IMB.4 and later carburetters. It differs from earlier
units in detail, principally in having fewer starting mixture
orifices 30 and 32 into the mixture duct 26.
2:8 Carburetter operation
Weber 26. OC
The new 500 station wagon is fitted with the Weber
26.OC carburetter which is of a horizontal draft design to
suit the engine which is fitted in the horizontal position.
The carburetter is fitted with a progressive action starting
device which enables the driver to adjust the mixture rich-
ness to the most arduous of starting conditions, and will
enable the engine to run eyenly until it reaches normal
operating temperature.
A dampened needle valve ensures a smooth running
engine as it is not affected by engine vibrations and there-
fore giving a constant fuel level in the carburetter bowls.
A secondary venturi is incorporated in the single casting
of the carburetter body.

Carburetter operation, starting device:

The petrol from bowl 23 (see FIG 2:13) reaches the
starting jet 37 through the duct 35. By operating the choke
lever 31 to the end of its stroke, the valve 30 is lifted from
its seat and brought to the 'fully open' position as shown
in diagram 'A' (FIG 2:13). Under these conditions the
valve 30 uncovers both the starting mixture ducts 28 and
29. With the throttle set in the idling speed position the
engine vacuum created by the operation of the starter
motor causes the fuel contained in the recess of jet 37 in
the jet and the reserve well 36 to be mixed with the air
coming from the air jet 38.
The mixture arrives through the ducts 28 and 29 at the
same time as air from holes 34, past the throttle so per-
mitting easy starting of the engine.
Key to Fig 2:12 A Cold starting position
2 Air inlet 21 Primary venturi
33 Valve 34 Mixture duct
42 Cover and cable support
air reserve well duct 47 Reserve well
F500
and adjustment,
A
FIG 2:12

Section of later starting device

B Warming up position
24 Secondary venturi
35 Air orifices 38 Rocker
43 Valve spring 44 Spring guide and retainer
48 Starting jet
FIG 2:11 Mounting flange modification: A earlier, B
later (dimensions in mm)
Once the engine has initially fired the starting device will
deliver a mixture whose petrol/air ratio is such that the
engine will run regularly even though it is cold. As soon as
the engine warms up this rich charge would be excessive
and therefore it becomes necessary to gradually ease back
the operation of the starting device. As this is occurring,
the valve 30 gradually covers up the mixture duct orifice 28
so as to weaken the mixture while by closing the duct 29
gradually. It also reduces the amount of mixture delivered
by the carburetter as shown in diagram 'B' (FIG 2:13).
B
C Normal running position
26 Mixture duct 27 Air bleed
39 Lever return spring 40 Control lever
45 Starting jet emulsion air duct
C
30,32 Starting mixture orifices
41 Control wire screw
46 Emulsion
41