Abstract: An adjusting screw of a carburetor comprising a threaded portion, an enlarged head portion and a reduced diameter portion located therebetween. A thin hollow cylindrical wall is formed on a link lever of the carburetor. After the adjusting screw is screwed into the threaded hole of the hollow cylindrical wall, the reduced diameter portion of the adjusting screw is cut. Then, the top portion of the hollow cylindrical wall is bent inward for irremovably fixing the adjusting screw onto the link lever.

Abstract: An adjust screw device for use with a carburetor of an internal combustion engine having stops for restricting the range within which the automobile user can readjust the idle R.P.M. by adjusting the adjust screw at the carburetor. The adjust screw device is composed majorly of a first adjust screw having a large adjustable range and a second adjust screw for fine adjustment, the physical position of the second adjust screw being changed by the adjustment of the first adjust screw. After initial adjustment of the first adjust screw by the manufacturer, further adjustment of the screw is completely blocked and the second adjust screw is then adjustable by the user only over a predetermined range.