I am a Sport Pilot CFI with over 500 hours of tail-wheel time in quite a few different models, but this one is really challenging

I have a new student with a really nice 1999 Kitfox 3 w/ 80hp 912

You could not ask for a more stable, gentle tailwheel plane when on the grass, but paved runways are a different story

The mains track straight and true but as soon as the tailwheel touches down it swerves radically from left to right, as it slows down it gets even worse

I have flown Kitfox’s before but I don’t remember any abnormal handling characteristics

When preflighting, the tailwheel assembly and associated cables & springs all appears normal

Any ideas?

(I previously mentioned this elsewhere in an unrelated post, but felt this question should be in the "General Discussion" area, if incorrect area moderator please move)