A small single cylinder 4 stroke gasoline engine varying capacity from 100cc to 500cc generally used for two wheelers has a wide range of load conditions. Such variation in load on engine demands variation in Transmission ratio at different vehicle speeds for optimum performance, drivability and Economy. A scooter has continuously variable transmission called as CVT which is generally centrifugally controlled with respect to engine speed as against that of series of manual gears used in motor cycle.The work aims at creating a mathematical model for controlling variation in transmission ratio of CVT by converting the generally centrifugally controlled CVT by electronic control. The objective is to implement the mathematical model with a novel electronic controlled CVT in a two wheeler engine for the improvement in performance. The mathematical model done through geometric calculations and modeling is discussed in details. The mathematical model is compared with the actual testing data to validate the calculations and results. Thus with this mathematical model and mechanism we can achieve a variation in engine transmission ratio as per load demand.The work explains the impact of mathematical model for controlling CVT ratio installed on the two wheeler engine and hence will resultant improvement in performance in terms of drivability and economy of a vehicle. On the whole it concludes that this mathematical model can be implemented on small engines for better performance.