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ADJUSTING THE CARBURETTOR
The carburettor of your FS-120S-E has been factory set for
the approximate best result, but the settings may, in some
cases, vary
slightly
in accordance
with
fuel and climatic
conditions.
If the desired
throttle response
is not obtained
after the
completion of the running-in period, the carburettor should
be re-adjusted as follows. Please refer to Photos 2 and 3.
Three adjustable controls are provided on this carburettor.
@
The
Needle-Valve:
For adjusting
the mixture strength
when the throttle is fully open.
@® The Mixture Control Screw:
For adjusting the mixture
strength
at part-throttle
and
idling speeds,
to obtain
steady idling and smooth acceleration to medium speeds.
è
The Throttle Stop Screw: For establishing the minimum
idling speed.
Mixture control screw
Needle
valve
Rotor guide screw
f-
Photo 2
E
1. Set the throttle
lever
1/4 open
from the fully closed
position
(see Fig. 3) and start the engine in the usual
way.
It is preferable to have the throttle only slightly
open, to avoid
unnecessarily high revolutions when the
engine starts.
2. Now
open
the throttle
fully and
gradually
close the
needie-valve
until the engine is running at its optimum
rp.m.
in the air.
The needle-valve setting at this time
will
be
1/8 to
1/4
open
from
the
maximum
r.p.m.
setting.
Note:
Make sure that the engine is fully "'run-in'' before operating it
continuously at full power.
(See RUNNING
IN section.)
3. Having set the needle-valve as described above, close the
throttle and run the engine at idling speed for approxi-
mately 5 seconds, then steadily move the throttle to the
fully open position by means of the throttle servo.
(a) lf, at this point, the engine hesitates before picking
up speed, with
a low-pitched
exhaust note and an
excess of exhaust smoke, it is probable that the idling
mixture is too rich.
In this case, it will be necessary
to turn the mixture control screw clockwise about 45
degrees.
(b) If, on the other hand, the engine hesitates or even
appears
to
cease
firing
for an
instant,
before
in-
creasing speed, it is probable that the idling mixture is
too lean.
In this case, it will be necessary to turn the
mixture
control
screw
counter-clockwise
about
90
degrees, then turn it clockwise 45 degrees.
Turn the mixture control screw 30 to 45 degrees at a time
in the early stages.
When the response improves, turn the
mixture control
screw
10 to 15 degrees at a time.
Carry
out adjustments progressively and patiently, remembering
the symptoms of rich and lean running, quoted above, until
the engine responds quickly and positively to the throttle.
4. The throttle stop screw is for fixing the minimum idling
speed.
If, after carrying out mixture adjustments, the
idling speed
is found
to be too high, the throttle stop
screw
should
be
turned
counter-clockwise
until
the
desired idling speed is obtained.
Note:
Once the correct carburettor settings have been established, it
should be unnecessary to alter them.
Such slight needle-valve
readjustments
as may
be required
to compensate
for varia-
tions in atmospheric conditions, will not normally affect the
other two controls.
Slight readjustments may be necessary
for optimum
performance
if different types of fuel, glow-
plugs or propellers are used.
In this case, begin by flying the
model with the needle-valve approximately
1/8 to 1/4 turn
open from the peak r.p.m. as a safety measure, then readjust
as necessary.
REALIGNMENT OF MIXTURE CONTROL VALVE
In the course of making carburettor adjustments, it is just
possible that the Mixture
Control
Valve may
be inadver-
tently screwed in or out too far and thereby moved beyond
its effective adjustment range.
lts basic setting can be reestablished as follows:
The basic (factory) setting is as shown in the main sketch,
i.e. with the shoulder portion 'A' exactly at a tangent to the
throttle rotor hole.
To return the Mixture Control
Valve to its original position,
first
screw
in the
Mixture
Control
Valve, while
looking
into
the
rotor
hole.
Then
gradually
unscrew
the
Mix-
ture Control Valve until 'A' is
precisely
tangential
to
the
rotor hole (i.e. so that 'A' and
'B' are superimposed)
as in
Throttle
'A
rotor
hole
an)
the main sketch.
B
Fig. 4
CARBURETTOR
CLEANLINESS
The
correct
functioning
of
the
carburettor
depends
on
its small fuel orifices remain-
ing clear. The minute particles
of foreign matter that are pre-
sent
in any
fuel
can
easily
partially
obstruct
these
orifices
and
upset
mixture
strength
so that engine
per-
formance becomes erratic and
unreliable.
=
It is recommended
that fuel is passed through a filter when
the tank is filled and that a good in-line filter is installed
between
the fuel tank and carburettor and, furthermore,
that this filter is frequently cleaned to remove dirt and lint
that accumulate
on the filter screen.
Finally, occasionally
remove the needle-valve holder from the carburettor, using
the
wrench
supplied, and
extract
any
remaining
foreign
matter
that
may
have
lodged
in the location
shown
in
Photo 3.
Throttle
stop screw
Dirt and fibrous
matter mostly
accumulate here.
Photo 3
VALVE CLEARANCE
ADJUSTMENT
Valve
clearances
are
correctly
set before
any
O.S. four-
stroke engine
leaves the factory and, in normal
use, will
seldom require adjustment.
However, if, after a considera-
ble amount
of running
time
has accumulated,
a loss of
power is detected, or if the engine has to be disassembled or
repaired
as a result of a crash, valve clearances should be
checked
and
readjusted
as necessary.
For checking and
adjusting the valve clearances, a valve adjusting kit, contain-
ing two feeler gauges and two wrenches, is available as an
optional accessory.
Note:
Valve clearances on this engine. must
be checked and reset
only WHEN
THE
ENGINE
IS COLD.
1. Remove
the
rocker
cover
by unscrewing
two
Allen
screws from the rocker box on top of the cylinder head.
2. Turn propeller until compression is felt, then turn it one
quarter turn and stop. Both valves should now be closed.
3. The
required valve clearance
is between
0.04 mm
and
0.10 mm (.0015
to .004 in.) measured between the valve
stem and rocker-arm.
Use the 0.04 mm
(thinner one)
and
0.10
mm
(thicker
one)
feeler
gauges
to check
clearance.
The 0.04 mm
feeler should pass through the
gap: the 0.10 mm gauge should not.
4. If the gap is found to be less than 0.04 mm or more than
0.10 mm,
carefully slacken
the locknut on the rocker-
arm
with
the 5 mm
wrench
supplied,
turn
adjusting
screw with 1.5 mm
Allen key to open or close gap, then
retighten locknut.
Finally, re-check gap and readjust if necessary.
IMPORTANT:
Incorrect
valve
clearances
may
cause
difficult
starting (due to valve not closing properly) or loss
of power (due to valve not opening sufficiently).
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