With big power V8's and single carbs they run into problems with even distribution between cylinders, hence they usually have to go for 2 like the pro stockers. Butterfly and injector per cylinder like a quad weber downdraft setup would be sweet, pity they don't allow electronic fuel injection.
I was under the impression that most bikes have efi now, i know the hypo ones like ninja's, R series yamas and gsxr zuks do.