Abstract: A small vehicle, such as a go-kart, which includes a power train unit including an engine and a transaxle which are attached to the frame of the vehicle as an integrated component. In this manner, easy installation of the engine and transaxle to the frame of the vehicle is facilitated. An adjustable engine mounting system is provided, which allows fine adjustment of the position of the engine to vary the tension of the belt drive which drivingly couples the engine and the transaxle. The transaxle includes a selective lock-out feature which allows an operator to lock out selected forward or reverse gears to thereby modify or limit the performance characteristics of the go-kart as desired to a particular application. Additionally, the transaxle includes a built-in differential which may be selectively locked out by the operator during running of the vehicle, in order to switch between “differential active” and “differential locked-out” positions.