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d) DIAPHRAGM CARBURETTOR WITH PRIMER
The carburettor with primer is characterised by the
absence of a choke and by the presence of a special
rubber pump, connected to the carburettor base cover
by means of a rubber tube (Fig 8).
The cover has a small hole (Fig 8, item A) to allow return
movement of the diaphragm after the lifting action of the
primer. Fitted immediately behind the inlet elbow is a non-
return valve which prevents petrol from flowing back to
the tank when the primer is used, thus ensuring that all
the fuel is injected into the venturi.
NOTE - (1) The use of compressed air may damage
this valve.
(2) The inlet needle should be held off its seat
for this operation.
If the inlet elbow is obstructed and prevents the passage
of air, remove the elbow by pulling and twisting motion,
bearing in mind the initial position for reassembly. By
blowing the reverse way to the petrol flow, it is possible to
clean the fine filter located in the elbow.
Refit elbow. After tapping it in by about one third, use
some Loctite or other adhesive, to ensure a petrol tight fit
when the elbow is completely inserted. (Fig 9).
Non-return valve fails to operate (brass type pressed
in valve).
After removal of the elbow, remove valve for replacement.
For this operation proceed as follows: (Fig 10).
- Tap centre hole A of valve with a 5/32 tap.
- Remove tap and, with a 5/32 screw nut and washer
(Fig 10), extract the valve by tightening screw in tapped
hole, retain the screw with a screwdriver, turn the nut
with a spanner. The valve will then be withdrawn by the
screw.
- Refit the new valve, seating it with the aid of a punch
which taps the valve squarely onto its seat. At this point,
check operation of valve.
- Refit the needle valve seat (Fig 11). Supply petrol by
means of a plastic pipe and check that petrol does not
escape from the valve (A of Fig 11), but readily flows
past the valve when the inner disc is held off its seat.
Fig. 10
Fig. 9
Fig. 8
Fig. 11
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