Weber Carburator Manual.pdf - Power by BMW E21

7-2
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Fig . 7.1 Single carburettor fitted to a four-eylinder V-engine
(Sec 1)
unit with both barrels feeding a common inlet manifold, the
most common arrangements being as fo llows:
1 One unit on a four-c ylinder in-line engine
2 One unit on 8 four-c ylfnder V engine
The ca rburettor iden tificatio n mark is located on the lower
flange outer surface.
2 Construction
The main body and cover of the carburettor ty pes covered
in th is Chapter (Ire of die-cast aluminium or zinc alloy (M azak)
construction. The mounting flange is machine d flat for fitting
purposes. The cover incorporates a mo unting flange for the air
9 Nozzle
35 Throttle valve
50 Choke valve
5 1 Spring
52 Lower extension
53 Lever
Part 2 Weber carburetors Chapter 7
cleaner assembl Vand is equipped w it h fou r mounting studs.
The throttle valves are of brass and the th rottl e shafts.
wh ich run directly in the carburettor body, are of steel.
All fuel and air jets are of brass construction and are
screwed into the main body ; the emulsion tubes are also of
brass.
Internal channels of th e main body and cover are mo stly
drilled and are sealed with lead plu gs wh ere necessary.
Single f uel float assemblies are fitted to 32 OFO, 32 OFE.
32 OFM, 32 OIF and 32 OAF types and are of brass constr ucti
on; two semi-f loats are fitted to remaining types and they are
of plastic or brass constr uction .
3 Operation
Fig . 7.2 Manual choke operation (Sec3J
Cold starting - manually operated choke
Refer to Fig. 7.2 and note tha t when the lever (53) is moved
to posit ion A, the choke valves (50) close the air intake. At the
same ti me the fast idle lever (55 ) partia lly opens the primary
t hrottl e valve (3 5).
Wh en the engine is cran ked, a rich mixt ure is draw n fro m
the nozzle (9) to facilitate starting. As soon as the engine fires.
the add itio nal vacuum causes t he choke valves (50 ) to partia lly
open , due to the off set pivot shaft , against the tensio n of the
spring (51).
As th e engine w arms up the control cable is pro gressively
shut, until at posit ion B the choke valves are fully open and the
primary throttle (3 5) is returned to its idli ng posit ion. The choke
valves (50) are held open by t he lever extension (52 1.
Cold starting - automatically operatedchoke
Refer to Fig. 7.3 and note tha t w hen the engine is cold and
the throttle pedal has been depressed once. the bi-metallic
54 Fast idle rod
55 Lever
52
f..-----'''''4- 54
A Cold starring position
B Fully open position