O.S. Engines 55AX - Manual (Page 17)

31
MIXTURE CONTROL VALVE ADJUSTMENT
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
degrees. 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.
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 this case, turn the Mixture Control Screw
counter-clockwise 90 degrees 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.
32
REALIGNMENT OF MIXTURE CONTROL VALVE
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 approx. 1.5turn. This is
the basic position.
SUBSEQUENT STARTING PROCEDURE
Once the optimum needle-valve setting has
been established (see page 29, Needle-valve
adjustment diagram) the procedure for starting
may be simplified as follows.
Open the needle-valve one half-turn (180
degrees) from the optimum setting.
Set the throttle one-quarter open from the
fully closed position, energize the glowplug
and apply the electric starter. When the
engine starts, re-open the throttle and re-
adjust the needle-valve to the optimum
setting.
When re-starting the engine on the same
day, provided that atmospheric conditions
have not changed significantly, it may be
practicable to re-start the engine on its
optimum(running) setting.
Note:
1.
2.