CropDuster,

Open the air-bleed screw slightly; about 1/8 of a turn at a time and retry to check the response.
An air-bleed screw is certainly not a "no low end adjustment possible" situation.
It is just a different way of doing it.

The OS.65LA has an air-bleed adjustment and it is by far better than the OS.61FX's "real" idle mixture needle.

Read the MAN 05/2003 engine shootout.