the invention contemplates an electrical network associated with a throttle - control potentiometer whereby a standard commercially available linear potentiometer having an given angle of electrical - resistance variation may be employed , over an entire lesser angle range of throttle rotation , to provide an output voltage which , for an initial fraction of throttle displacement , is a predetermined substantially linear variation of a given input voltage , and which , for the remaining fraction of throttle displacement , remains substantially constant at the level of the upper end of the linearly varying fraction . a feature of the invention is that the slope and extent of linear variation are selectable , without modification of the linear potentiometer .