They represent a key element of engine reliability and, in particular, the cooling system. Rubber belts connect the water pump to the rotation of the axle, which in turn is driven by the engine through a rack and pinion transmission. The pump circulates water in the radiator: the greater the rotation speed of the axle and, therefore, of the kart, the faster the water flows. Obviously, it needs to be a good quality water pump, not one that cavitates (i.e. creates air bubbles in water inside the pump, which affect the circulation of the cooling liquid). The pump was inside on the “old” KF engine. Nowadays, OK engines have gone back to fitting externally mounted pumps (as was the case on 100 cc engines), which therefore require rubber bands and also means simpler engines, as well as facilitating work on the water pumps themselves.