O.S. Engines 21XZ-M - Manual (Page 7)

12
Marine Head
Crankcase
Mounting Lugs
Exhaust
Cover Plate
Carburetor Type 21D
Crankshaft
BASIC ENGINE PARTS
Ball Bearing (Front)
Glow Plug RP7
13
CARBURETOR CONTROLS (21D)
The Needle-Valve:
The Mixture Control Screw:
Two adjustable controls are provided on this
carburetor.
For adjusting the mixture strength when the
throttle is fully open.
For adjusting the mixture strength at part-
throttle and idle speed, to obtain steady idling
and smooth acceleration to mid speeds.
Mixture Control Screw
Mixture
Control Valve
Mixture Control Screw
Needle Valve
BASIC POSITION OF MIXTURE CONTROL SCREW
(Mixture Control Valve)
Thick
Lean
shown in the sketch. (In case of 30% nitro fuel)
In case of 65% nitro fuel, basic position should
be approximately 45 degrees turned left from
the center. Mixture gets lean when the Mixture
Control Screw is turned right, while mixture gets
rich when the Mixture Control Screw is turned
left. With a model boat, adjustments vary with
combined various factors such as climatic
conditions, fuel, muffler, etc. Therefore, Mixture
Control Screw position varies with each model
and set-up, and it is normal if the Mixture Control
Screw position is off center.
As delivered, the Mixture Control screw is
positioned at approximately the center as
45