O.S. Engines 61RX-H WC - Manual (Page 17)

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.
The general course of adjustments procedure is
shown in the ADJUSTING CHART and is correct for
a fuel containing 20% lubricant and 10-30%
nitromethane.
Bear in mind that fuels containing relatively large
percentages of power-boosting nitromethane operate
at richer mixture settings than are needed for mild
fuels and will, therefore, require the High-Speed
Needle Valve to be readjusted accordingly. The type
and percentage of lubricant used is also a factor
here, as noted later in these instructions.
This carburetor is not fitted with a throttle stop
screw. Instead, idling speed is adjusted by
means of the throttle trim lever on the trans-
mitter. • Idle Mixture Control Screw. A special technique is
required here. If intending to make an adjustment
(e.g. 90˚ in the same direction, before returning it to
the new setting. If this procedure is not followed,
movement of the throttle rotor may become stiff,
resulting in undue loading of the throttle servo.
Existing Position
Richer Leaner
Desired Position
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.
lf, at this time, 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. lf the
mixture is extremely 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 an excessively prolonged warming-up
period.
ADJUSTMENT PROCEDURE
1.
16