This may seem strange but when i raced and i got front end chatter you could sometimes cure it by adjusting the rear. I believe it is a case that by adjusting the rear ride height/pre load it alters the way the front reacts due to weight distribution. Might be worth a phone call to a suspension expert like Maxton.

I expect someone will shoot me down in flames but it seemd to work for me on both my KR1S and TZ250!
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MC21 300
Aprilia RS250 track bike