I'm not sure where the mixture screw is, I also want to find that, i think mines running too rich, and i think the little black thing with a black wire coming out is a pre heater or somthing like that. I've got an exploded diagram of the weber and it points out the mixture screw, but the line ends up at a corner, rather than a screw, so i was kinda hoping someone could upload an image and circle the screw.