BSA B33 - Carburettor Adjustment and Decarbonising; Carburettor Adjustment; Engine Decarbonising

Carburetter.
So long as
the engine
contidues
to
perform
satisfactorily,
the carbuetter fu best
left
alone,
pa.ticularly
by the
experienced dder.
The
only
adjustment in
which
the owner is
lik€ly
to
be interested is the
pilot
air søew
(Fig.
l6a),
(Fie.
16b 'Monobloc') which controls the slow
running mixture.
This is set before the machine leaves the
works,
but
tbe
best
setting may vary slightly to suit rider's
requircments,
or different iocalities.
Tuming
the
pilot
air screw inwards
enriches
the mixture
and unsøewing
weakens it. A richer mixture
gives
a slower
and mole
reliable tick-over, but it is
naturally
undesfuable
to have
the mixture too rich. even with the throttle
practically
closed-which
is,
of
course, the throttle
position
for
tick-over-so the best
way to set the
pilot
arl
sqew
is
to
screw
it in until
the mixturc is obviously too rich, and
then
unscrew it until
the setting is
just
right, atrd
further
unscrewing increases
the
9icEqy[spggd
unduly. This may
seem
complicated,
but the efrect of alteritrg the setting is
vely
noticeable,
and the
dd€r
will easily detect the
symptoms.
It is doubly
important to avoid over-richness
of the
tick-over setting
if much ddiDg is done on small throttle
openings for
this is what is kao\tn as 'ruDning
on the
pilot'
and
if the
pilot
setting is too ch, the
getreEl
petrol
consumption
will be advenely affected.
The running
mixture can only be altered
by adjusting
the
height of
the needle in the throttle valve
or by fitting
a main
jet
of
diferent size. Such alterations
should not
be made
except for very special
purposes,
as dictated
by
abnormal
requirements and only then on expert
advice.
DECARBONISING
TIIE
ENGINE
Decarbonising
and 'top overhaul'
of an engine is
exfemely
simple, but it should only
be carried out wben
the
engine
reålly rceds it. The usual symptoms
are
an
increased
tendency to
'pink'
(a
metallic
knocking when
under
healy load) due to the building-up of
carborl on
the
top of
the
piston
and inside of cylinder
head; a
general
falling-off
of
power
noticeable
mainly
on hills,
atrd
the
engine inclined to run hotter
than usual.
Befote
cor
nencing
geDeBl
djsmantling, rotate the engine
until
cilp
t N0Tcl{
AIllusIMElfI
NEtDtE
p0slTloll.
CANBUIEMN
fip0mE
AIR
su0E.
AN
siuDE.
MAtN
l,,l$BIu"o*''
Fig.l6a.
Th.
standad
carbtlrettet
39