Help me please Carb problem

[monkeymanjaso...]

Hi every one can any obe help me iv got a dt 125 1986 and it wont tick over you have to hold the throtle slightly if you let it go then it will die iv turned the fuel mixture screw the idolin screw both screws on the carb and it still just wants to die all the time it was running perfect a few days ago and now i have all this problem...when you turn the screws it dont do anything but when you turn them all all the way in it will tick over for about 5mins and you can rev it and it will come back down a few mins later it will over rev but wont come down if anyone can help me it will be great sometimes it over revs to mainly all the time or just dies constantly iv also changed the cylinder gasket and head gasket so no leaks thanks.......