John,
I used to ride with KX250 forks (before Acme started tuning my suspension), and the steering head bolt is probably the wrong size (depending upon the bike years). On my 1999, the 500 bolt was smaller than the 250 bolt. The solution? I used 10mm shim stock to make a round spacer that I tapped in the gap between the tripple clamp hole and the bolt. Total cost was less than $1.00.
If this is your problem, this should solve it.
Rick