I have a gasgas 280 - 03 and i have some problems to get a good idling... when the bike is chocked the idling is fine when i put the chocke down it sounds very strange like uneven idling.... i have tested to turn the large screw on the side of the carbourator....is that screw both for idling and petrol-air mixture???

Does that screw have any standard setting ??

When the chocke is down i think the throttle is to sensitive....it goes up in rpm when i bearly thouch the trottle???

Sounds like a pilot jet blockage or an air leak. Most likely the pilot jet though. Take it out, clean it well and blow out with compressed air. Then try it again.