O.S. Engines FS-120S III - Manual (Page 16)

• Feeler gauge 0.04mm
Valve clearances are correctly set before any O.S. engine
leaves the factory and, in normal use, will seldom require
abjustment. However, if,after a very considerable amount of
running time has been amassed, a loss of power is detected,
or if the engine has been disassembled for repair, these
clearances should be checked and reset as necessary. For this
purpose, a valve adjusting kit comprising two feeler gauges, a
5mm ring spanner (box wrench) and a 1.5mm Allen key, is
supplied with the engine.
Start the engine, open the throttle fully and set the needle-
valve slightly rich (30-45
°
) from the highest r.p.m. setting.
Close the throttle to the idling position. Allow the engine to
idle for about 5 seconds, then reopen the throttle. The
engine should accelerate smoothly back to full speed.
If, instead, the engine responds sluggishly and emits an
excess of white smoke from the exhaust, the idling mixture
is too rich. Turn the mixture control screw approx. 45
°
clockwise to lean the idling mixture.
On the other hand, if the engine hesitates before picking up
speed or even ceases firing completely, the idling mixture
is likely to be too lean. Turn the mixture control valve 90
°
counter-clockwise to substantially enrich the mixture, then
back again 45
°
clockwise.
IDLING MIXTURE ADJUSTMENT
In paragraphs 3 and 4 above, the 45
°
total movements are,
of course, approximate. It will be necessary to fine-tune the
mixture control screw 10-15
°
at a time to reach the best
setting for optimum throttle response.
Continue re-checking the idling mixture setting until the
engine responds smoothly and positively to operation of
the throttle at all times.
In the course of making readjustments, it is just possible that
the mixture control screw may be inadvertently screwed in or
out too far and thereby moved beyond its effective range.
The factory setting can be re-established as follows:
Set the throttle at the fully closed position.
Now carefully rotate the mixture control screw clockwise until
it stops. Finally, turn the mixture control screw back exactly
2.5 turn.
Realignment of Mixture Control Screw
1.
2.
3.
4.
5.
6.
VALVE ADJUSTING
The kit comes in a plastic case and includes:
(Code No.72200060)
• Feeler gauge 0.1mm
• Hex. key 1.5mm
• Wrench 5mm
15