http://www.osengines.com/manuals/index.html
Here you can find all manuals from OS engines, settings will probably in it.
If it's the OS .12 CV-R
High speed needle: 2 full turns open
Low speed needle:
rotating carb: put the head of the screw even with the carburator body and then turn in 0.5 turns.
sliding carb: put the head of the screw even with the carburator body and then turn in 2.5 turns.
Rotating carburator opening approx 1mm at idle
Sliding carburator opening: 0.3 - 0.5 mm at idle