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The point of the jet needle is tapered to
adjust
the flow of fuel-air mixture in
accordance
with the opening of the
throttle valve. During high-speed driving (the opening of the throttle valve is above 3/4) the fuel is measured by the
main jet
and
mixed with the
air
measured by the
air
jet to make
a
fine spray of fuel-air mixture of good quality for de-
livery to the
engine.
2.
Adjustments.
When the
engine
has dual
carburetors,
it
is
the
prerequisite
for full
engine
performance to maintain the equal operation
of each carburetor.
The following items
should
be followed
cautiously
and accurately.
2-
1.
Adjustment of choke wire.
Make
adjustment
with some degree of play for the
starter
wire so that the starter plunger of each carburetor may not
rise when fully
closed.
However, the play must be adjusted without excess and deficiency,
since
the concentration of
the fuel-air mixture during the initial
starting
will get confused if the degree of play is so excessive that the starter
plunger
cannot
be
opened
to its full width.
2- 2.
Adjustment of throttle wire.
With your eye or plug gauge, adjust the opening of each throttle valve from the side of the air cleaner with the throttle
wire
attached and
the throttle open. With your
eye,
you can
adjust
accurately by matching the corner of the cutaway
of the throttle valve with the upper surface of the main
bore.
After adjustment, be sure to fasten the cable adjuster
lock nuts as well as the starter wire.
2-
3.
Adjustment of idling and
synchronization.
(a)
Set
the air
screw
of
each
carburetor
at
the standard return number and then fasten the throttle stop screw of
each
carburetor evenly,
setting
the number
at about
1,000 rpm which is a little higher than normal idling speed.
(b)
Warm up the engine completely.
(c)
Find
out
and set
the position where the number of rpms of the engine becomes maximum by opening or clos-
ing the
air screws one
by one about 1/2
each
time. In this
case,
be sure to use a tachometer.
(d)
Return each
screw
of the throttle valve
evenly and
set
at
the normal number of rotations of idling.
(e)
Find
out and set the position once more where
engine
rotation becomes maximum by opening or closing the
air screws one
by one
about
1/16
each
time.
(f)
If the number of rotations has
changed
in the
adjustment
mentioned in paragraph (e),
set
once more at the
normal number of rotations of idling by means of each throttle
stop
screw.
(g)
Remove the plug
cap
of each cylinder and check whether the down percentage in the number of rotations of
the
engine
is constant or not at that time. If not, return the throttle stop screw on the side where the down
percent-
age is larger and adjust so as to make the down percentage constant.
(h)
In the last step, operate for
5-
10 minutes by idling.
If
the rotations of the engine are normal during that
time, the adjustment is complete. If abnormal, remove the ignition plug and check the condition of combustion. If
the combustion seems to be somewhat over, return the air screw, and if somewhat under, fasten the air screw.
2-4.
Adjustment in accordance to the
altitude and
the temperature.
The density
of
the air varies according to the altitude and the temperature. It is necessary that the delivery of the fuel
in the
carburetor
should be
changed
according to the
change
of the density of the air.
During idling
and
low-speed driving, make adjustment
according
to the procedures mentioned in paragraph
2-3.
20
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