The percentage of oil to be added to the petrol to obtain the mixture for your kart varies exclusively according to the dictates of the manufacturer of the engine being used. In fact, based on its characteristics, the engine manufacturer establishes the right percentage of oil to use. Otherwise, the percentage of oil to be used can be imposed, again in agreement with the engine manufacturer, by the organiser/promoter of a race which also indicates the type of petrol (FIA approved or road distribution network).