ABSTRACT A tractor engine operating on variable speed and constant speed, wherein the tractor comprises: a foot-operated accelerator (112, 212) and a hand-operated accelerator (114, 214) for selectively actuating a speed governor (116, 216), a fuel injection pump (118, 218) connected to the speed governor and tractor engine coupled to an application load (122, 222), characterized in that a mode selection switch (102, 202) is connected to the fuel injection pump and the tractor engine via an electronic module (104, 204) for selectively operating the tractor engine on a constant speed mode CSM (106, 206) for a standstill condition of the tractor for operating an agricultural implement at constant PTO speed or a variable speed mode VSM (108, 208) based on the application load connected to the tractor engine and for performing normal farming operations by the tractor. The fuel injection system is operated mechanically or electronically. The speed governor is operated mechanically or electronically or a combination of mechanical and electronic operation. FIGURE 3a.
