I tried to get things as step by step as possible.Don't worry about not having the parts for this because most of the things on this site I myself can't build because of lack of parts. How ever I do recommend buying the Racers 20+ Building kit to get the wheels you see on the Kart. Please rate.
Step 1: Step 1
These are the back wheels.Follow the pics and read my notes.
Step 2: Step 2
This is the spoiler and the front wheels.
Step 3: Step 3
This is where you attach the front wheels to the spoiler.
Step 4: Step 4
These are optional parts that you can put on if you like them.
Step 5: Step 5
This is how to wind it up.