To make a go kart can be fairly complex. Your first step is to gather your materials. Obtain a welder. If you do not know how to weld, you will have to hire or seek help to complete the project. The welds should be good quality, with proper penetration and uniform beads. Otherwise the stability will be off and the last thing you want is for your kids cart to fall apart while moving. That would be pretty serious road rash.Draw out your plans for the go kart. The size you make it will depend on the age of the driver. For young drivers, about 30 inches wide by 50 inches long will work, but for older kids or adults, you will want about 40 inches by 72 inches. Gather and find all the parts. You may be able to salvage parts from an old riding lawnmower or a junkyard or even a go kart found at a yard sale. For steering linkage sketch and Cut the metal tubing according to your design, and weld it together. For more strength, use gussets at all corners. Assemble your steering linkage, using the 1/2 inch steel rod for linkages, and the 3/4 inch for your axles. To make the 90 degree bends in the 3/4 rod, you may have to use a torch to heat the steel. Take your time with steering, because it is very important. Build your rear axle with your straight piece of 3/4 steel rod, and two bushings attached to your frame. Use washers and cotter pins drilled through the axle to keep the assembly in position. Attach the drive pulley on the axle prior to mounting the axle in the bushings. You can either use a set screw to hold it in position, or weld it directly to the axle, but it should be aligned with the pulley on your engine. a flat piece of 3/16 inch steel plate to the rear frame to mount your engine. Place the engine on the plate, and mark the holes for mounting bolts so that the engine pulley lines up with the drive pulley on your axle. Attach the throttle cable to the hand throttle, or a linkage for a foot throttle which is optional. Build your seat and floor boards out of plywood lumber or metal, roughly you can decorate or make as comfortable as you want but this is the basic design.