Having provisionally set the idle mixture, the next
step is to adjust the mixture for hovering flight.
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 High-Speed
Needle Valve clockwise. Do not close the High-
Speed NeedIe Valve more than the recommended
initial adjustment (3 to 4 clicks) at a time, keeping
it a little on the rich side at this stage. DO NOT
touch the Medium Speed Needle Valve.
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 High-Speed Needle Valve counter-
clockwise.
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 Screw counter-clockwise to enrich
the mixture.
2.
When satisfactory hovering flight has been
achieved, land the modeI again and re-check the
engine's idlling qualities.
After about 10 seconds of idling, open the throttle
to 'float' the model. lf the transition is smooth, the
idle mixture is O.K. If the symptoms of either rich
or Iean running are observed, readjust the Idle
Mixture Control Screw accordingly.
NOTE: With this carburetor, neither the Idle Mixture
Control Screw adjustment, nor the Medium Speed
Needle Valve adjustment has any effect on mixture
strength when the throttle is fully (or almost fully)
open.
Throttle Opening
Fully Closed
1/3
2/3
Fully Open
Fuel Flow
Maximum
Minimum
Adjustment range of Idle Mixture
Control Screw
Adjustment range of Medium
Speed Needle Valve
Needle Valve too
far open
Needle Valve too
far closed
High Speed Needle
Valve Setting varies
according to the curve.
17
