Choke Unloader
A diaphragm device for partial release of choke butterfly valve is used to prevent excessive choking. It is operated both by vacuum and a mechanical lever and spring. When choke is operated, butterfly valve is closed to restrict air flow and provide a richer air/fuel mixture for cold starting. As soon as engine fires, vacuum partly opens butterfly valve against action of calibrated spring. Vacuum downstream from throttle valve activates diaphragm device which further weakens mixture and engine will progress smoothly to normal running.