So, I have this 98 WR400F carb (39mm Keihin FCR). There are 2 parts, of which I do not know what they are for. The 1st part has a red circle in the picture: The parts sheet says "diaphragm assy", but a diaphragm for what? The second part has a red ellipse in this picture: It has an on/off switch, and is connected to the diaphragm. Is this something like a hotstart? I'm puzzled! Thanks!