I ALWAYS follow the manufacturer needle recommendations and for the DA50 this is what they recommend and if DA says this is the way then do what they say.... DA is DA and they know how it's done!
http://www.desertaircraft.com/manuals/DA50-Manual.pdf
Needle Adjustments
• The needle farthest from the motor is the “High End” needle. The needle closest to motor is the
“Low End” needle. Turning the needles in/clockwise “leans” the fuel mixture. Turning the needles
out/counter-clockwise “richens” the fuel mixture.
• Settings will vary with altitude, temperature, humidity, fuel, carb variances, etc. A "general" starting
point for the DA50 is: 1 5/8’s open on the Low needle, 1 7/8’s open on the High needle.
• Adjusting either needle can have a slight effect on the other. Example: Leaning the low needle can
"slightly" lean the high rpm range.
• Adjust the High End needle to peak rpm. A tachometer can help, but remember that the RPM
normally drops a little bit after every start due to residual heat build up. Don’t lean the mixture any
more than necessary. If the rpm steadily drops at full throttle or fades on long vertical maneuvers,
the motor is too lean and is overheating.
• Adjust the Low End needle until you achieve a smooth idle and a reliable transition to high throttle.
Generally if the motor “stutters” or “coughs” in the mid range or when the throttle is advanced, the
low end needle is too rich and possibly even the high end needle. If the motor dies quickly, the low
end is probably lean.
• Don't set the needles overly rich to protect the engine. Operating the motor overly rich not only
reduces power, it creates other problems such as poor transition, pre-mature carbon build up, fouled
plugs, excessive exhaust residue, sticking rings, airframe vibration, and overall rough running.