As for balancing tires on a sprint kart, it depends on the tires. If you are experiencing a front end shake, look at the front tires for balance and how true they spin. On occasion I’ve had front tires shake violently at and above 40 mph and once I had a rear tire take over 2 ounces(ran out of weights) to get any where near balanced.
It just depends on what you are experiencing, front end shake at speed, look for tire balance and trueness. Massive shaking on kart, look for the same in the rear.