I don't know you brake-type but, usually, there are two choices.
  1) You add 'pad shaped' pieces of metal (shims) bought for that purpose (bought for your SPECIFC bake system) BEHIND each pad as the wear increases which, effectively, takies up the 'slack' caused by the wear of the pad.
  2) The caliper itslf is made in two halves. The halves themselves are separated by 'shims' and you REMOVE these as the pads wear.
  There are other methods but uyou need to check your kart to see which it is. If there are no 'between the halves' shims, then it'll PROBABLY be the 'behind the pad' shims.
  The final choice.....? Fit new pads!
  Ian
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