O.S. engine MAX-105HZ-R Instruction Manual page 17

OS arama
2. 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. If the
engine smokes excessively 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 Needle
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.
If, on the other hand, hovering is not stable and
response to the throttle 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.
When satisfactory hovering flight has been achieved,
land the model again and re-check the engine's idle
qualities.
OS creme
3. Now adjust the High-Speed Needle Valve to
achieve the best performance when the model is
flying at full throttle. If, at full throttle, acceleration
is poor, the exhaust unduly smoky and the model
fails to reach expected straight line speed, the
mixture is too rich and the High-Speed Needle
Valve setting will need to be reduced.
If, however, after smoothly accelerating to
satisfactory high-speed straight and level flight,
power is lost when the model is pulled up into a
climb, the mixture is too lean. In this case, land the
model immediately and readjust thw High-Speed
Needle Valve to a richer setting.
4. Having now found the optimum setting for the
High-Speed Needle Valve, re-check the engine's
idle performance, fine tuning the Idle Mixture
Control Screw, if necessary, to perfect the idle.
32
After about 10 seconds of idling, open the throttle to
'float' the model. If the transition is smooth, the idle
mixture is O.K. If the symptoms of either rich or lean
running are observed, readjust the Idle Mixture
Control Screw accordingly.
= Needle Valve too N
Ë far open
3 !Adjustment range of Medium High Speed Needle
5 Speed Needle Valve Valve Setting varies
according to the curve.
n Needle Valve too
s far closed
=
°
=
š |
5
š LL
5 Z= Control Screw ;
Fully Closed 18 23 Fully Open
Throttle Opening A
NOTE: With this carburetor, neither the Idle
Mixture Control Screw adjustment, nor the
Medium Speed Needle Valve adjustment will have
any effect on mixture strength when the throttle is
fully (or almost fully) open.
5. Now re-check hovering performance It may be
found that (with the High-Speed Needle Valve
now set for optimum full-throttle performance)
hovering will reveal symptoms of slightly lean
running at medium speeds. DO NOT touch the
High-Speed Needle Valve.
It is at this point that the Medium Speed Needle
Valve, previously set one and a half turns open,
may be brought into operation. Open the Medium
Speed Needle Valve 30 degrees, or 3-4 clicks,
then fine tune until the optimum hovering
performance is obtained. If on the other hand,
hovering reveals rich running, close the Medium
Speed Needle Valve gradually until the optimum
hovering performance is obtained.
33