I'm not sure if your talking the 400 or 650. There is an adjustment under the seat on the left side of the 650. I wouldnt call it a knob though. It helps in adusjting the drivers butt rest.Squeeze the handle/knob and you can slide the butt rest forward or backward and release to lock in place.
You do have me curious though and I will have a better look for any other knobs the next time I pop the seat.
A forum community dedicated to Suzuki Burgman motorcycle owners and enthusiasts. Come join the discussion about performance, modifications, classifieds, troubleshooting, maintenance, and more! Open to all 200, 400, and 650 models!