Idling problem????

I have a 2000 X reg Gilera Coguar (it has a copy of the Honda 4 stroke single cylinder engine (old cb125 single) with which I'm having a problem. The bike starts and runs fine but I have a problem with the idling speed. Sometimes it will tick over fine and other times like when I pull up to traffic lights and pull in the clutch, it may run for a few seconds then peeter out and cut out. Other times when the clutch is pulled in (at traffic lights, junctions etc.) it's like the idle speed has been turned up and it revs higher. It will also when standing at idling speed, randomly start revving higher than normal and then start revving higher and then dropping down to normal (ish) again and then start to fade out again and then cuts out. I have stripped down, cleaned and reassembled the carburettor but it still does it. I've checked and oiled the throttle cable and that's fine yet it still does this. I was considering fittinga new needle and jets to see if that would solve the problem, any suggestions?????????? Can anybody help me please as this is starting to drive me mad. Thanks in advance, John.