O.S. Engines 40C Carb - 25683000 - Manual

INSTRUCTIONS FOR O.S. TYPE 40C AUTOMATIC CARBURETTOR
This carburettor, as fitted to the O.S. MAX-46FX-H RING helicopter engine, incorporates an automatic
mixture control device which ensures that the engine receives a correctly balanced mixture of fuel and air at
all throttle settings. It ensures steady revolutions and a smooth response for reliable helicopter ascent and
descent.
Needle Valve
Rotor Guide Screw
Mixture Control Valve
(Mixture Control Screw)
Throttle Lever
Photo 1
Two adjustable controls are provided on this carburettor.
• The Needle Valve:
When set to produce maximum power at full throttle, the
Needle Valve establishes the basic f u e l / a i r mixture
strength. This is then maintained by the carburettor'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 acceler-
ation to medium speeds. The Mixture Control Valve has
been factory set for the approximate best result. First,
run the engine as received, and re-adjust the Mixture
Control Valve only when necessary.
A PROVISIONAL SETTINGS (see ADJUSTMENT CHART)
• Open the Needle Valve 2 turns from the fully closed
position. (Be sure to use a muffler-pressurized fuel feed.)
Note: This carburettor is not fitted with a throttle stop screw.
Instead, idling speed is adjusted by means of the throttle trim
lever on the transmitter. This enables the full r.p.m. range,
from idling to full power, to be controlled by the throttle
stick, and then allows the engine to be stopped, from the
transmitter, by closing the throttle completely with the trim
lever. Set up the throttle linkage as follows:
With the transmitter throttle trim lever fully retarded, adjust
the throttle servo linkage so that the throttle rotor is (a) fully
open when the transmitter throttle stick is fully advanced and
(b) fully closed (i.e. engine stopped) when the stick is fully
retarded.
The idling speed is then set by advancing the throttle trim
lever to the point where the engine runs, steadily and
reliably, at the desired idling speed.
RE-ESTABLISHMENT OF MIXTURE CONTROL VALVE-
SETTING
In the course of making carburettor adjustments, it is just
possible that the Mixture Control Valve may be inadvertent-
ly screwed in or out too far and thereby moved beyond its
effective adjustment range.
Its factory setting can be reestablished as follows:
1. Disconnect the throttle linkage by removing the con-
trol rod from the throttle lever.
2. Fully close the throttle.
3. Turn the Mixture Control Valve clockwise gently until it
stops, while keeping the throttle fully closed. Do not
over-tighten the valve.
4. Turn the Mixture Control Valve 2-1/2 turns counter-
clockwise from the above position. This is the basic
(factory) setting.
ADJUSTMENT PROCEDURE
The following adjustments are approximately correct when
using a fuel containing 25% lubricant and 10—30% nitro-
methane.
Bear in mind that fuels containing relatively large per-
centages of power-boosting nitromethane operate at richer
mixture settings than are needed for mild fuels and will,
therefore, require the Needle Valve to be readjusted
accordingly. The type and percentage of lubricant used is
also a factor here,as noted later in these instructions.
B As a safety measure, first check the transmitter controls,
including the throttle stick and trim lever positions, and
hold the main rotor securely before starting the engine.
C Warm the engine by allowing it to idle for about 30
seconds. If the engine stops, advance the throttle trim
lever slightly to increase the idling rpm. Then open the
throttle sufficiently to 'float' the model above the ground.