How to fix Death Wobble 1

alright guys so I just got an 18 KTM 125 SX,First ride I realized it had short bars and I know that by going wider would help a little bit and just is more overall comfortable. Then the suspension is set to 140,I’m 105lbs And a C rider, yes I know you guys will tell me to fix it and I’ve already done almost everything I can to suspension,And I get really gnarli head shake/Tank slapper all the time at least twice every lap in braking bumps, would a Damper help to fix this? Otherwise what else can I do,and I also have the head Nut already way to tight