You shouldn't have a white fill, the fill is empty according to the toolbox. Do you have only the two objects on the artboard - the background image and the black path? You set the stroke width in the Stroke pane - should be under the Window menu. What the outline stroke command does is turn the line, with a stroke applied, to a path running around the edges of the stroke, filled with the original stroke's colour - presumably so that when you take that into C4D and lathe it the result will be a double-sided bulb, rather than a skin around a bulb-shaped void. Visually, nothing should change, but the stroke colour should be set to none (the black box at the bottom of the toolbox in your image) and the fill colour to black (the box with a line across it, behind the stroke colour in your image).