THE AMAL MKII CARBURETOR
How
1Ft
operates
When the engine i,s idling, mixture is supplied from the pilot jet system,
then as the throttle slide is raised, via the pilot by-pass. The
mi
xture is
then controlled by the tapered needlle working
in
the needle jet and
fi
n
all
y
by the size of the main jet. The pirot system
is
supplied by a pilot jet,
which is
detachahle. The main jet does not spray directly into the mixing
cham
ber
but discharges through the needle jet into the primary air
chamber
and the fuel goes from there as a pertol-air mixture through the
pri
mary
air choke into the main air choke.
This primary air choke has a compensati
ng
action
in
conjunction with
bleed holes
in
the needle jet, which serve the double purpose of air-
compensating the mixture from the needle jet and allowing the
fuel
to
provide a well, outside and around the needle jet, which is available for
snap acceleration.
ADJUSTMENT
OF
CA
'RBU'RETOR PARTS
Throttle
stop
screw
This
screw
should be set
to
open the throttle sufficiently to keep the
engine running at a slow tick-over, when the twistgrip
is
closed.
Pilot
air
screw
To set the idling mixture, this screw should
be
set in
to
enrich or out
to
weaken, normal number of turns out from full
in
is about
2'12.
The screw
controls the suction on the pilot jet by metering the amount of air which
mixes with the
petrol.
Needle
and
needle
jet
Machines
are delivered from the 'factory with the needle
in
the correct
location.
00
not attempt
to
readjust the setting without expert advice.
Throttle
valve
cut-away
The
amount of cut-away
is
recorded by a number marked on the throttle,
viz
2928/2V2
means
throttle type 2928 with No. 2V2 cut-away; a larger
cut-away
such as 4 gives a weaker mixture or a smaller such as 2 gives a
richer mixture.
For settings see Useful Data on Page
6.
Air
filter
The air filter has two elements consisting of surgical gauze bound with
metal gauze. To remove the elements detach the outer covers by means
of
the centre fixing bolts and withdraw the elements. The elements may
be washed
in
clean petrol and then finally cleaned with a jet of
compressed air.
32
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