O.S. engine GT33 - Needle Adjustments

OS. mans
The slow speed needle is effective through the high
speed range, while the high speed needle is not effective
in the low speed range. Both needles are effective in the
mid speed range, while the slow speed needle is the most
effective. (Refer to the diagram below.)
More
^^ High Needle `
N Ñ Effective Range \
Fuel Flow
/ Slow Needle Effective R
/
/
ange /
Less —
1/2 Fully open
Throttle Opening
3/4
Carry out the needle settings as follows.
lll Adjustment on the ground
1. Set both needles at two turns open from the fully closed
position.
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OS aam
NEEDLE ADJUSTMENTS
. Start the engine. Open the throttle valve slowly until fully
open and run the engine for 10 seconds to warm the
engine.
. Set the throttle stick 3 clicks advanced from the bottom and
measure rpm with a tachometer and write it down.
. Close the slow speed needle approx. 30 degrees and
measure rpm with a tachometer and write it down. (Be sure
to adjust the slow needle only after stopping the engine.)
. Repeat step 4. to locate the slow speed needle position
where maximum rpm is achieved. Open it approx. 90
degrees from this position. This is the basic slow needle
position.
. Open the throttle valve fully and measure rpm with a
tachometer and write it down.
. Close the high needle approx. 30 degrees and measure
rpm and write it down. (Be sure to adjust the high needle
only after stopping the engine.)
. Repeat step 7. to locate the high needle position where
maximum rpm is achieved. Open it approx. 30 degrees
from this position. This is the basic high needle position.
. Set the throttle trim on the transmitter so that the idle rpm is
approx. 1,800
(approx. 1,600rpm when idle down function is used).
10. Warm the engine for 10 seconds with the throttle fully
open, then idle the engine for 5 seconds, then quickly
open the throttle fully. Make sure the engine does not
respond sluggishly to increase rpm nor hesitates before
picking up speed or even ceases firing.
11.If the engine responds sluggishly to increase rpm, the
mixture is too rich due to the slow speed needle being
open too far. Close the slow speed needle approx. 15
degrees. Repeat this procedure until the engine
accelerates smoothly. (Be sure to adjust the slow speed
needle only after stopping the engine.)
12. If the engine hesitates before picking up speed or ceases
firing, the mixture is too lean due to the slow speed needle
being open too far. Open the needle approx. 15 degrees.
Repeat this procedure until the engine accelerates
smoothly. (Be sure to adjust the slow speed needle only
after stopping the engine.)
Bl Adjustment with flight
13. If the rpm drops or the exhaust sound weakens when
vertically climbing from level flight with full throttle, the
mixture is too lean. Land the model and open the high
speed needle approx. 15 degrees. Repeat this procedure
until the engine sound is smooth.
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14. If, on the other hand, exhaust sound is irregular when
vertically climbing from level flight, the mixture is too rich .
Land the model and close the high speed needle approx.
15 degrees. Repeat this procedure until the sound in level
flight is steady.
15. If the power drops gradually or exhaust sound weakens
(overheating symptom), when performing torque roll and
hovering, the mixture is too lean. Land the model and
open the slow speed needle approx. 15 degrees. Repeat
this procedure until power remains steady.
16. If the above symptom is not detected with prolonged
torque roll and hovering but sluggish to increased rpm
when the throttle is fully opened abruptly, the mixture is
too rich. Land the model and close the slow speed needle
approx. 15 degrees until sluggish rpm increase
disappears.
Note
Generally, a gasoline engine is sensitive to a lean mixture
compared with a glow engine, and will stop without
warning hesitation and stops with overheating.
It is recommended that the engine be run with a slightly
richer mixture.