MX bikes have suspension and padded seats. Its pretty much a solid path from the motor to your body in a kart, which has neither. Isolating the pipe won’t do much as the motor itself is mounted solid to the frame, which mounted solid to the seat. A Tillet padded seat (Model T7, I think) is an option if it’s really driving you nuts and you can find one that fits. Believe it or not, a TaG kart with a Leopard motor is even worse. You’ll get used to it.