O.S. Engines FS-52S - Manual (Page 18)

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.
4.
5.
6.
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 richen the mixture, then back again
45
°
clockwise.
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.
Its basic position can be found by first rotating the
Mixture Control Valve unit its slotted head is flush
with the carburettor body. The valve is then screwed
in exactly 1 turn to re-establish the original setting.
Realignment of Mixture Control Screw
First rotate the Mixture
Control Valve until its
slotted head is flush
with the carburettor body.
Mixture Control Valve
Carburettor Body
VALVE ADJUSTING
ALL O.S. four-stroke engines have their valve(tappet)
clearances correctly set before they leave the factory.
However, if, after many hours of running time have
been logged, a loss of power is detected, or if the
engine has to be disassembled or repaired as a result
of an accident, valve clearances should be checked
and readjusted, as necessary an O.S. Valve Adjusting
Tool Kit is available as an optional accessory.
17