RE: DA50 - Hard to Start, Idle Unreliable
It sounds to me like you're setting needles appropriately, fatten the top a little from peak and the low end just rich enough to cover the transition.
So... IMHO it's time to look into other possible problems like an air leak somewhere in the fuel system? Especially if things had been fine until recently, that suggests maybe something has come loose, cracked, etc. Have you checked all your fuel line connections? Carb still bolted on tight? Could even be somewhere in the case, if it's sucking air somewhere you'll definitely have problems getting it to run right.
As I said, I don't own a DA but I think it ought to be able to idle down more than what you're seeing.
There are a bunch of guys here with much more experience than I who have already responded, maybe they'll chime in again with this additional information from you.