MG Midget J1 1933 Instruction Manual page 75

Petrol from the float-chamber is led to a jet, the size of whose orifice-
and consequent delivery-is regulated by means of a tapered needle attached
to the lower end of a piston controlled bs the suction from the engine.
As
this suction increases the needle is gradually withdrawn from the jet, enlarging
its effective opening and permitting
i t
to pass more petrol.
T h e jet is so mounted that i t may readily he moved up o r down relative
to the tapered needle, in order to weaken o r strengthen the mixture over the
whole working range, by a lever operated from the mixture control lever on
t h e b n e a r side of the dash. This control provides an enriched mixture to
ensure easy starting and even running when the engine is cold. T h e mini-
mum jet opening can accurately be set by means of the adjusting nut, which
forms an abutment for the enlarged head of the jet.
T h e carburetter is extremely simple, and its adjustment is equally simple
if i t
is r'emembered that the jet is of a fixed standard size and cannot be altered.
T h e only possible adjustm'ent, other than the slow-running adjustment, is
the fitting of a new needle of a different size. Since a needle of the correct
size is fitted at the W o r k s before the car is dispatched, this adjustment should
not he required, and the suction chamher is therefore sealed.
Copper packing
washer
Spring
Copper pack~ng
washer
Brass washer
&
T O ~
half jet
4
bearing
h ~ o r k gland washer
L
Brass washer
half jet
bearing
-
Cork nasher
_
Cork gland washer
dJet adjusting nut
Sources of Trouble. T h e r e are only four troubles which may affect the
functioning of the
S.U.
carburetters.
1.
T h e piston may be sticking and not functioning properly.
2.
T h e r e may be dirt o r water in the c a r b ~ r e t t ~ e r .
3.
T h e float mechanism may have become deranged, and the carburetter
is in consequence flooding.
4.
T h e carburetters may require synchronising.
Piston Sticking. T h e suction piston consists of the piston proper forming
the c h o k e ; the suction disc, into which is inserted the hardened and ground
piston rod working in a hearing in the suction c h a n ~ b e r ; and a tapered n,eedle
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