O.S. Engines 50SX - Manual (Page 24)

MIXTURE CONTROL VALVE ADJUSTMENT
REALIGNMENT OF MIXTURE CONTROL VALVE
With the engine running, close the throttle and allow it
to idle for about five seconds, then open the throttle
fully. If, at this point, the engine is slow to pick up and
produces an excess of exhaust smoke, the mixture is
too rich. Correct this condition by turning the Mixture
Control Screw clockwise 15-30˚. If the mixture is
excessively rich, engine rpm will become unstable:
opening the throttle will produce a great deal of
smoke and rpm may drop suddenly or the engine
may stop. This condition may also be initiated by
excessively prolonged idling.
If,on the other hand, the mixture is too lean, this will
be indicated by a marked lack of exhaust smoke and
a tendency for the engine to cut out when the throttle
is opened. In this case, turn the Mixture Control
Screw counter-clockwise 90˚to positively enrich the
idle mixture, then turn the screw clockwise gradually
until the engine regains full power cleanly when the
throttle is reopened.
Carry out adjustments patiently until the engine
responds quickly and positively to the throttle control.
Note: Mixture Control Valve adjustments should
be made in steps of 15-30˚ initially,
carefully checking the effect, on throttle
response, of each small adjustment.
In the course of making carburetor adjustments, it is
just possible that the Mixture Control Valve may be
inadvertently screwed in or out too far and thereby
moved beyond its effective adjustment range.
Its basic setting can be re-established as follows:
Close the throttle rotor gradually from the fully
opened position until it is just fully closed.
(Do not turn further.) Then, screw in the Mixture
Control Screw until it stops. Now unscrew the Mixture
Control Screw as indicated below.
50SX
40 · 46FX
approx1 turn
61FX
91FX
approx turns
approx2 turns
2
1
2
1
2
1
23