if its only running without the air filter its one of 2 things. Your air filter offer changing as its blocked. Or your mixture is too rich. Also have you balanced the carbs?

Yeah all the o-rings in the carbs were done!

I figured it was running way to rich - but now the running is quite tempermental - itll start if left for a long period of time but it wont run for very long!

Also it wont start just without the airbox anymore, so i guess its maybe fowled up the plugs a bit?

How do i go about leaning it out, is it the pilot screw and the neddles i need to adjust?

i can never remember where people are. If your in the uk pm me your number and i'll give you a call mate