DESCRIPTION    OF    CARBURETTER.

FUEL FEED. The float chamber (s) and the mixing 
chamber (h) are in two separate pieces, and bolted 
together by flange (n1) and studs (r)   between the 
flanges are a petrol filter gauze (m) fitting into recess 
(m1) and a paper washer (n), making a petrol tight 
joint between them. The carburetter contains only
one jet (k] which is well submerged in the fuel ; it is 
screwed into the end of the needle jet (j), and is easily 
accessible by undoing the cap (l), under the mixture 
chamber. The fuel from the float chamber flows 
through the main jet (k) and finds its level in the 
needle jet (j), which just protrudes into the mixing 
chamber under the throttle. The petrol pipe connec-
tion under the float chamber is horizontal banjo (u) to 
take a rubber pipe ; it can be swivelled round in any 
direction and locked by nut (w).
The petrol level is maintained by a float (p] and needle 
valve (v), the needle is not adjustable. The needle is 
attached to the float by a wire bow on the top of the 
float which engages in a groove in the needle. 
The fuel passage from the float chamber to the jet 
chamber is very large and protected by the gauze 
ring (m) fitting into the recess (ml).

MIXTURE CONTROL. The throttle (g) is of the. 
piston type sliding up and down ; it has two slots 
down its length, the deeper one for engaging the control 
cable and the shallower one to slide over a screw to 
locate its position. The throttle has a cutaway on the
air intake side at its end nearer the jet —which cutaway 
can have different angles to operate for the purposes 
of mixture control at lower speeds.
The throttle carries a taper needie (f) which protrudes, 
into the needle jet (j) : there are several positions for 
this needle in the throttle so that the mixture may be 
adjusted correctly by its relation to the throttle 
opening. The needle travels up and down as the 
throttle is moved because the needle clip (e) rests on 
the throttle and is held there by the throttle spring (d). 
The throttle needle is accurately ground to a suitable 
taper and slides in the needle jet which has an accurate 
bore, the differences in diameters providing a means 
of controlling the flow from the main jet to correct 
the mixture at mid-throttle openings. 
In conclusion; a correct mixture is maintained at all 
throttle openings, viz. ;—
    At full throttle, by the size of the main jet.
    At small openings, by the throttle cutaway and, in 
           intermediate positions, by the position of the needle.
   For starting from cold the air filler is provided with
           strangler shutter.
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NOTE-The jet (k) and the needle jet (j) etc. are too small to be
interchangeable with those in the larger AmaL range of carburetters.

INDEX TO EXPLODED VIEW OF CARBURETTER 308.

(a)  Cable adjuster.                           (p)   Float (bottom feed).
(b)  Adjuster lock nut.                     (q)   Coverscrews for fl. cham.
(c)  Mixing chamber cover.              (r)   Holding studs and nuts
(d)  Throttle spring.	                           for float chamber.
(e)  Throttle needle clip.                   (s)   Float chamber, bottom
(f)  Throttle needle.	                           feed.
(g)  Throttle valve.                             (t)   Needle valve seat and
(h)  Mixing chamber body.                            petrol connection.
(j)  Needle jet.                                     (u)   Petrol pipe banjo.
(k)  Main jet.                                       (v)   Float needle.
(l)  Jet cover.                                      (w)   Petrol pipe banjo nut.
(m)  Filter.                                           (x)   Outlet clip.
(n)  Fl. cham, flange washer.           (y)   Outlet clip screw.
(o)  Cover for float chamber.           (z)   Outlet clip nut.

The small screw in the side of the throttle chamber is not seen :
this screw acts as a guide for the throttle.

HINTS & TIPS ON CARBURETTER TUNING.
Provided the petrol-oil mixture is to the engine-makers'
specification and is well mixed and that there is an 
ample flow to the carburetter, any incorrect carburation
must be due either to too weak or too rich a mixture. 
If the mixture is suspected to be rich make sure that 
the float chamber is not flooding : if flooding, clean out
all impurities in the petrol pipe and float chamber. 
Before " tuning " the carburetter, decide at what 
throttle opening any fault appears. A weak mixture 
is evident by spitting in the carburetter or by inability
to open throttle. A rich mixture is evident by lumpy
running, smoky exhaust, and oily sparking plugs.
        If the error appears at :- 
Full throttle, alter the main jet (k). 
At small throttle openings, select a throttle  (g) with 
   different cutaway.     A  larger cutaway  weakens the
   mixture  and  the smaller one  richens it. 
At half throttle, adjust the needle position.  Lowering 
   the  needle   (f)  weakens the mixture ; raising  it 
   richens the mixture.
When the above has been attended to. any correction 
to the slow running must be done by the cutaway of 
the throttle.

FUEL DRIPPING FROM PETROL PIPE 
CONNECTION UNDER FLOAT CHAMBER.
The hexagon nut (w) under the float chamber should
be tightened gently and firmly only to secure, in a petrol
tight manner, the banjo petrol pipe connection (u)
between its washers : it must never be overtightened 
with a large spanner, otherwise this will result in 
breakage. If petrol appears to drip from here it may 
be seeping from the end of the rubber pipe which is 
pushed over the serrated end of the banjo connection (u).
Alternatively, the drip may be due to flooding over the 
float chamber cover (o) due either to excessive vibration 
or to impurities (grit, fluff, etc.) lodging on the needle 
valve seating and so preventing the needle valve (v) 
from closing tight. There is an air vent hole in the rim 
of the cover (o) which must be clear.
Genuine flooding can only be due to a bent float needle, 
an excessively worn groove in its conical head, float-
bow jumped out of needle groove or a punctured float.

 25M/2/51. W.	               Printed in England.