If the leach is fluttering, it's not tight enough.

So, either

1, Move the block forward to tighten it.
2, Move the pole lower to tighten it.
3, Add a leachline to your kite if this will correct it.
4, Add a twinning line so you can change the sheeting angle without moving the block.
5, The kite is FUBAR and you need to buy a new one.