Select a bike kit and components. You can purchase an all-inclusive kit (example in Resources below) that will provide you with all the necessary materials to build a pocket bike. You also have the option of purchasing your bike's components separately or in bundles. For example, some bike kits do not include a motor, so you would have to purchase the motor separately. This motor can be purchased pre-assembled, or you can purchase a small motor bundle that will include all the necessary materials to build the motor yourself.
Paint your frame. Be sure to clean and apply primer before painting.
Put together and mount (install) the wheel assemblies. The front and rear wheel assemblies are put together in a similar way. Put the axle collars on both sides of the front and rear wheels; however, you will need to also fit the 72-tooth sprocket on the rear wheel, on the outside of the axle collars. Be sure to fit 72-tooth sprocket on the same side as the smaller sprocket on your transmission you will install. Place both wheel assemblies between fork legs. Push the axle completely through the wheel and screw in the bolts to secure the assembly to the frame. Tighten all bolts, first with your hand, and then with a wrench.
Install the engine. Put the transmission on top of the engine and place the entire unit on the engine mount. Connect the chain between 72-tooth back sprocket and the smaller transmission sprocket by looping the chain between the teeth of the two. Move the engine mount along the length of the frame to find a position were the chain is fairly tight (but not too tight); mark this position on the frame. Weld the engine mount to the frame using this mark. Bolt the engine to the engine mount.
Install the throttle and brake levers. Bolt the securing clamps of these levers to opposite handlebars. Run the throttle and brake cables, along the frame, to the respective motor and braking mechanisms. Connect these cables according to your product's manufacturer specifications. Attach the kill switch on the frame next to the throttle. Connect the wire of the kill switch to any other wire on the engine block by splicing them together --- secure the exposed wire with wire tape.