ENGLISH
19
LOW SPEED NEEDLE TUNING
1.
Adjust the high - speed needle for the current conditions.
2.
Allow the engine to idle for 10–15 seconds. Rapidly advance the throttle from idle to full open.
If the engine transitions with no hesitation, the low-speed needle is adjusted perfectly. If the
engine slowly responds to throttle change and gradually reaches peak RPM, the low-speed
needle is too rich. Lean out the low-speed needle (turn clockwise) 1/16 turn and test again.
If the engine immediately stops running, the low-speed needle is lean. Richen the low-speed
needle 1/16 turn and test again.
3.
When the low-speed needle is adjusted correctly, check the high-speed needle setting again.
4.
When you are satisfied with the needle settings, you should not need to adjust the lowspeed
needle again. The low-speed needle setting is mechanically controlled and does not change
with atmospheric conditions.
The best indication that your engine is tuned properly is the color of your spark plugs when re
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moved from the cylinder. A nice dry tan color is an indicator that the fuel mixture is correct and
burning well. Anything else (wet plugs, or carbon deposits) generally indicates you are running the
engine too rich.
Once the engine is running reliably at full (open) throttle:
1.
Lean the high-speed needle 1/16 of a turn at a time.
2. Wait 2–3 seconds for the engine to respond. Radial engines do not respond immediately to
tuning changes.
• If there is an increase in RPM: Lean the high-speed needle an additional 1/16 turn and wait
for the engine to respond to the tuning change. If there is no increase in RPM after the
change, turn the high-speed needle back to its previous position.
• If there is a decrease in RPM: Richen the high-speed needle 1/8 turn and wait for the engi
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ne RPM to stabilize.
3.
Repeat Step 2 until you determine the maximum RPM with the fuel and propeller you selec
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ted.
4.
Richen the high-speed needle so when full throttle is applied, the engine rpm will be steady
(not drop off) after reaching its peak RPM. Richening the high-speed needle allows the RPM to
increase when the airplane is flying.
HIGH SPEED NEEDLE TUNING
Low-speed needle adjustment controls the fuel/air mixture at idle and the quality of the transiti
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on between idle and wide open throttle.
LOW SPEED NEEDLE ADJUSTMENT
