Its more like an enricher circuit. A separate circuit on the inboard side that essentially dumps lots o fuel past the idle inlet. Pretty sure. I would have to go peruse the Bing manual again to be sure of the particular pathway details, but its basically a fourth fuel metering circuit, used only at startup because it would flood the thing otherwise.
"Why BMW? You like to suffer? My sister, she has five kids, no husband. You come over?"