24
ADJUSTMENT
A
The following adjustments are approximately correct
when using a fuel containing 18-25% 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 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 equipped with a throttle
stop screw. Instead, idle speed is adjusted by
means of the throttle trim lever on the trans-
mitter.
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.
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.
B
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 idle speed is then set by
advancing the throttle trim lever to the point where
the engine runs, steadily and reliably,at the
desired idle speed.
25
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 Valve 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.
lf, on the other hand, the mixture is too Iean, this
wiIl be indicated by a marked lack of exhaust
smoke and a tendency for the engine to cut out
when the throttle is opened. ln this case, turn the
Mixture Control Valve counter-clockwise to enrich
the mixture.
D
E
Hover the model and actuate the throttle to
observe response over the medium speed range.
lf the engine smokes excessiveIy and throttle
response is poor, the mixture is too rich ; in which
case, land the model and turn the Needle Valve
clockwise. Do not close the NeedIe Valve too
much, keeping it a little on the rich side at this
stage.
lf, on the other hand, hovering is not stable and
response to the throttIe is over-sensitive, or if the
engine tends to overheat, this indicates that the
mixture is too lean and should be corrected by
turning the Needle Valve counter-clockwise.
H
I
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 idle rpm. Then
open the throttle sufficiently to 'float' the model
above the ground.
C
Turn the Mixture Control Valve 15 degrees at a
time.
Having provisionally set the idle mixture, the next
step is to adjust the mixture for hovering flight.
F
G