The detailed procedure for the service of a carburettor is always
specified by the manufacturers and varies in the case of different types. However,
the general procedure and the points of caution are given below.
To remove the
carburettor from the engine, first of all, remove the air cleaner and disconnect
the throttle and choke lineages. Next, disconnect the vacuum advance unit and
any other connections that may be there. After that loosen the flange nuts and
remove the carburetor gently.
Dismantle the carburettor and clean each and every component
in the petrol. Detailed inspection of each part is then done and the faulty ones
are replaced, after which the carburettor is reassembled and the flange bolts tightened.
Remake the different connections in the order reverse to that done for
removing.
The most important precaution is that the jets should never be
cleaned with wires etc. rather they should first be cleaned with petrol and
then with a blast of air. Secondly, you must work with clean hands, otherwise
while assembling; the dirt from your hands will again go into the carburetor. Further,
it must be remembered that any adjustments to the carburettor should only be
done once it is first ascertained that the other components of the fuel system
are working all right; otherwise, the engine performance will not improve.
However, the common
adjustments and their procedure may be outlined as given below:
Idle adjustment
There is an idle adjustment screw provided in the carburettor. Screwing
in the same decreases the idle port area and hence decreases the engine speed. The
screw is adjusted till the engine runs smoothly at the required speed.
Generally, this is done by screwing-incompletely and then opening back by one or two turns. Another
method for idle adjustment, which is precise, involves attaching a vacuum gauge to
the inlet manifold and adjusting the idle screw till maximum vacuum is obtained
on the gauge.
Throttle adjustment
On releasing the accelerator pedal throttle valve should be
completely closed, while on pressing the pedal fully, it should be in full open
position. This may be checked and if not found correct, the linkage may be
adjusted, as provided for in the manufacturer’s manual.
Other adjustments
Apart from the idle a throttle adjustments, the other
adjustments that are provided in some carburettors are for accelerating the pump,
metering rod, floats etc. They may be performed as laid down in the manual.
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