Weber Carburator Manual.pdf - Power by BMW E21

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Fig. 4.7 A bad case of corrosion in a Weber
40 IDA 3C carbureto r
6 Cleaning
Th is is poss ibly t he most important aspect of overhauli ng th e
carburetor as dirt or sediment can lead to many diverse malfunctions.
It should be carried out in a w ell ventil ated area and suff icie nt
precautions should be taken to prevent the poss ibility of fire.
The carbureto r bo dy and covers may be cleaned with a
deqreasant, but only after removing all compo nents such as fiber and
rubber washers and seals which may be adversely affec ted. All traces
of gasket shou ld be removed from th e flange faces and the internal
channels shou ld be blown clear to remove th e dec reasant. It is
advisable to com pletely immerse th e components in carb ureto r
cleaner as an extra precaution.
The remaining carbureto r co mponents shou ld be cleaned in
carbureto r cleaner and allo wed t o dry on a clean t ray. In extreme
ca ses, th e use of pain t thinners w ill remov e th e mor e obsti nat e
accumulation of dirt and sediment.
7 Inspection and repair
Wit h all components cl eaned and set out, th ey must now be
inspected for wear and deterioration, in order to decide which are fit for
furth er service, which have to be repaired and wh ich must be renewed.
Spec ial overhaul procedures are given in the reievant chapter of
this manu al bu t the fo llo wing sect ions give gene ral procedures
app licab le to all carburetors.
8 Carburetor body and covers
Note: The body and. on some types, the covers are the only parts of
the carburetor whic h cannot be supplied as spares and therefore,
where these items are damaged beyond repair, a new carburetor must
be obtained.
1 Chec k internally and externally for cracks (refer to Fig. 4.5). These
are most iikely to be .found in the vicin ity of the flange mounting holes
and are due to overt ightening or excess ive vibrati on. On aluminum
alloy carburetors it may be possible for a welding specialist to carry out
a suitable repair, provided that none of the internal jets and passages
are affec ted . However, great care must be taken to prevent distortion.
Carburetors mad e from zinc alloy (Mazak) cannot be repa ired in t his
way and will either require replaceme nt parts or a new carburetor.
2 Check the flange faces for flatness using a straight-edge (refer to
Fig. 4.6). If any undulation or disto rtion is evident, lap the flange on a
sheet of fine emery cloth placed on a surface plate. Where app licable,
the carburetor covers may be checke d and recti fied using the same
procedure.
3 Check all tapp ed (internaily threaded) holes for th e condition of
Part 1 Introduction Chapter 4
Fig. 4.8 Removing a spindle in a St rombe rg carburetor
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the t hread. It will be obse rved that the more frequently used threads
are fitted with brass inserts and these do not normally deteriorate. but
where the t hread is tapped directly into the main body the threads may
fractu re. To repair the latter type of t hread, an insert (sometimes called
a Helicoil or Cross insert) must be fitted. This is a job best entrusted to
a suitably equipped machine shop . An alternative method of repairing
the t hread is t o dr ill out t he thread s completely and th en ta p an
ov ersize t hread, but thi s is only possible in some cases, as t he
attach ing component must be non-standard and it may be necessary
to drill adjacent components oversize. '
4 Sc rap e awa y any co rros ion wh ich may have attacked the
carburetor meta l (refer to Fig. 4.7). This will normally be found in the
vicinity of the float chamber on carbureto rs which have been out of
service for a long time. Finish the surface with fine emery cloth but take
care not to enlarge any internal bores or channels as this may affect
the calibration of the carburetor.
5 Clean any carbon deposits from t he carburetor barrels using a
curved scraper but ensuring that the barrel walls are not in any way
damaged. On differential ty pe carbu retors it will be fo und that t he
primary barrel is particularly susceptible to carbo n build-up which will
ad versely affect the carb uretor perform ance if not removed. Aft er
clean ing , the barrels may be polished lightly with meta l polish but
make sure that all traces of the polish are removed w hen the op eration
is com pleted.
6 Where a piston type acceierator pump is fitted, check the bore in
the carburetor body for scoring and damage. Although the bores are
inserted on assembly they cannot be obtained as a spare, and unless a
machine shop can effe ctively repair a faulty bore, a new carburetor
must be obtained .
7 Where app licable, check the cond ition of all st uds fitted to the
carburetor body and cover and renew them if necessa ry.
9 Vent uris and chokes
1 Check the auxiliary venturis and chokes for da mage; depending
on w here it is, min or d amag e may be removed w ith a fine file and
emery cloth, ot herwise renew them.
2 Using a t ire pump, b low t hrou gh the aux iliary vent uri internal
channel and nozzle to make sure th at it is unobstructed.
3 Where fitted, check that the iocating springs are intact and firmly
fitted to the auxiliary venturi and choke.
10 Throttle spindles and ch oke spindles
1 Check t he t hrottle spindles for wear by tempo rarily relitting them
to the body and moving them laterally. If wear is evident, an oversize
spindle should be obtained and the bod y reduced as described in the
relevant chapter of this manuai (refer to Fig. 4.8).
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