O.S. Engines 21RG-MX - Manual (Page 13)

CARBURETTOR CONTROLS
The Needle Valve:
When set to produce maximum power at full throt-
tle, this establishes the basic fuel/air mixture
strength. This is then maintained by the carburet-
tor's automatic mixture control system to cover the
engine's requirements at reduced throttle settings.
The Mixture Control Valve (Mixture Control Screw):
For adjusting the mixture strength at part-throttle
and idling speeds, to obtain steady idling and
smooth acceleration to medium speeds. The Mix-
ture Control Valve has been factory set for the ap-
proximate best result. First, run the engine as re-
ceived, and re-adjust the Mixture Control Valve only
when necessary.
Two adjustable controls are provided on this carburettor.
●
●
Needle-Valve
Mixture Control Valve
(Mixture Control Screw)
Throttle Lever
Fuel Inlet
Rotor Guide Screw
■ REALIGNMENT OF MIXTURE CONTROL VALVE
In the course of making carburettor 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 reestablished as follows :
Nozzle
Throttle Rotor Hole
Mixture Control Valve
(Mixture Control Screw)
The basic ( factory ) setting is
as shown in the main sketch, i.
e. with the shoulder portion 'A'
exactly at a tangent to the throt-
tle rotor hole. To return the Mix-
ture Control Valve to its original
position, first screw in the Mix-
ture Control Valve, while look-
ing into the rotor hole.
Then gradually unscrew the
Mixture Control Valve until 'A' is
precisely tangential to the rotor
hole (i.e. so that 'A' and 'B' are
superimposed) as in the main
sketch.
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