Well bike is sorted ;D
Looked in the Haynes manual apparently the throttle cable is in 3 parts and splits at a junction top part to twist grip, one from junction to carb and the other to the autolube which syncs with the lower cable for carb.
who everhad the bike before hadnt adjusted the lower carb cable properly so it had no free play so keeping cable or rather the slide up by about 8mm so thats why it wouldnt go below 4-6krpm.
though the slide sounded to be hitting the bottom of carb it wasnt, only the idle speed screw. sussed it when i took air cleaner cover off looked down the air intake to carb and saw it at least the carb had a good clean out 3 times lol