Whilst there are not any specific detailed plans you can download and build your kart to, there are quite a few guidelines and sketches that can be used as a starting point. Ideally all karts are a unique expression of the owner, each individually crafted to mimic or be inspired from the CycleCars of the turn of the last century. However not everyone has an automotive manufacturing background and so a basic chassis and drivetrain design from which they can then base their creations is a good idea.
The classical CycleKart design is known as the Stevenson design. This name is attributed to the guy that penned it and is the easiest style of kart to build. It has straight chassis rails, welded together with a slight taper from the rear to the front. The passenger compartment is generally a plywood box that sits between the rails. The bodywork is an extension of this basic box in whatever style the owner is trying to achieve.
The classic 'Stevenson' cyclekart design
There are also many variations on this basic design with profiled chassis and more ornate bodywork but the basic wheelbase and track of the kart remains essentially the same. There is no real limit to what you can do as long as your CycleKart follows the basic design outline as detailed in the technical section
You can find some additional plans and discussions on chassis design in the forums HERE