Pls check the bristle-picker on your machine at first.
Bristle-pickers are like these:
Bristle-picker takes bristles out from the bristle-box and conveys them to the bristle-mouth to be tufted into holes.
On bristle-picker, there is a hole of which the size is very important. The bigger the hole is, the more the bristles are tufted into a hole; the smaller the hole is, the fewer the bristles are tufted into a hole.
Consequently, if operator wants to change the quantity of bristles tufted into holes, he just needs to adjust the size of the hole on bristle-picker accordingly.