Norton 19S - Maintenance

slightly close the air lever when there should
be a slight falling off of speed indicating a
reasonably correct mixture. If maximum speed
is obtained before the throttle is fully open,
then a larger main jet is required; similarly
if there is an increase in speed with the air
lever slightly closed.
2nd SLOW RUNNING.
Having fixed the main jet, set the throttle
adjusting screw to provide a fairly fast idling
with the twist grip in the fully closed position
and the ignition (where manually controlled)
set for best slow running. Screw out the
throttle adjusting screw until the engine begins
to falter; now adjust the pilot air screw in or
out as necessary to make the engine run evenly
and faster. Lower the throttle adjusting screw
further to reduce engine speed until a position
of the pilot air screw is found at which the
engine runs evenly and steadily on the smallest
throttle opening.
3rd THROITLE VALVE CUTAWAY.
With the throttle valve about a ¼ open
(marking the twist grip if necessary in order
to readily find this position whilst riding) note
whether there is any spitting (indicating weak-
ness) or jerky running under load (indicating
richness). In the former event try screwing
in the pilot air screw slightly and if this is
ineffective, a throttle valve having less cutaway,
i.e., stamped with a lower number and the
reverse for jerky mnning.
4th THRO'fl'LE VALVE NEEDLE.
With the throttle about ¾ open and the
needle in a low position try the machine for
acceleration. If results are poor and partially
closing the lever provides improved conditions,
raise the needle a notch or two until the best
position is found.
5th ~HECK IDLING.
To ensure that subsequent adjustments have
not upset the condition.
PHASES OF AMAL NEEDLE JET CARBURETTER
THROTTLE OPENINGS
I
Up
to j open fromjro!openl !to I.open Jco rull open I
PILOT JET THROTTLE NEEDLE- MAIN JET
CUT-AWAY POSITION SIZE
2ND & 5Tl-f )RO 4rH 1sr
SEQUENCE
OF TUNING
Pig. 20
81. MAINTENANCE.
Clean periodically by dismantling and wash-
ing in clean petrol, cleaning out all holes by
blowing. Whilst dismantled examine throttle
valve needle and fl.oat needle for wear and all
fibre washers, renewing as necessary. Check
that throttle valve is not unduly worn in the
mixing chamber body.
82. RICH MIXTURE.
Indicated by black exhaust smoke, excessive
soot on plug, lumpy running, petrol blown
back from air intake.
Assuming that carburation has previously
been satisfactory, suspect:-fl.ooding due to
punctured fl.oat, dirt on fl.oat needle seating
or worn needle or seat. Worn throttle valve
needle or needle jet, air cleaner choked.
83. WEAK MIXTURE.
Indicated by spitting back, poor accelera-
tion, overheating, erratic slow running or
improved performance with air lever partly
shut.
Again assuming carburetter has been cor-
rectly set, suspect:-fuel blockage, either main
supply or within carburetter. Worn inlet valve
guide, air leaks at engine carburetter connec-
tion, worn throttle valve, loose jets.
LEGSHIELDS
84.
A standard set of these Legshield fittings
comprises:-
2 Legshield Blades.
30
2 Legshield Blade Brackets.
2 Legshield Blade Brackets Back Plates.
4 ¼" pins and nuts for above.
1 Hom Bracket extension plate with ¾" pin
and nut.