Hybrid gokart

Hello friends..!! I'm working on a hybrid gokart. Which will b based on electical drive(by MOTOR) as well as mechanical drive(by IC ENGINE) . But i'm little confused about the mechanism that what cheap n simple mechanism i use at the place of transmission so that firsty power is given by motor & after a certain speed it will given by the engine while kart is in running position. HELP ME ON THIS TOPIC . You can contact by reply here or by email on - rahulmishra.mishra81@gmail.com