need a bit of help

runs fine under normal conditions
but on full throttle have teribble miss fire
let of the throttle a touch black smoke then its of
changed leads plugs dizzy cap arm
had turbo problem put a nother one on since then i have had this missing
smells like it is running slightly rich as i am taken her to spec one over the weekend any surgestions would be great will leave it with you all
many thanks in advance