thanks for all the input guys, think i might be heading in the right direction now. after scouring my parts bins i came accross a spare carb with slightly diferent jets in. For the moment i have swaped the pilot jet which seems to be working, i also swaped out the worn slide and played around with the needle. Seems to be ok at the mo, still a little dark when putting round the garden, but good when getting it in to the mid and top end.
Had a convesation with the mikuni oz fellas and managed to come to some conclusions based on the fact that the further i turned the air/fuel screw out the higher the revs got. I was told this would indicate a too big pilot, the more i thought about it the more it made sense being that the plug indicated a too rich mixture. I dont know about you but a normal setting for the screw would be around 1 and a half turns to start then fine tune when engine is hot. Normally you would not be able to tweek more than half a turn in either direction before the engine starts to bog then you set it in between. whell you could wind it out a long way and the thing kept going!
You learn something new every day i guess?