Cheeseburger! Cheeseburger! Cheeseburger! When that doesn’t work, bolt lead weights to the seat of the kart. You can buy them from kart shops. They’re available from 2 to 8 pounds. If you know of a local plumbing supply near you, they should have 5 pound lead bricks. You’ll have to drill them for a 5/8’s bolt and either double nut them or drill the bolt for a cotter key. On the 8 lb weights, you’ll probably be required to use two bolts. Most track I know of require the weights to be painted white. You can move the weights up or down the seat for to help in chassis tuning.
I found some lead bricks that go up to 26lbs it is 2″ x 4″ x 8″ is there anyway something that large can be illegal?