It could be a lot of things, Headset adjustment (or alignment), structural (cracks starting) or a number of other causes or simply "quick steering"" geometry, To make bikes steer quicker, one can 1) steepen the headtube and fork, 2) increase the fork rake (not intuitive but trust me) or 3) shorten the overall wheelbase (this has much less dramatic effect). A lighter front wheel, especially rims and tire/tube will also speed up steering.
1) and 2) are tightly linked and can have a dramatic effect with small changes.
I raced a bike with a 75 degree headtube angle. Largish frame. It had the same fork as the smaller frames of that model that came with more "normal" headtube angles. By modern standards, a lot of rake. The steering was so quick I could not comfortably ride no-hands the first month and a half of the season but as my riding got smother and I trusted the bike more, I found I could ride it no-hands anytime and in fact loved that I could steer around stuff easily no-hands. Now on that bike, a less than perfect headset flat out didn't work! My Peter Mooney is a far more forgiving bike (shallower head tube and less fork rake) and I rode the Campy HS that Peter installed for about 25,000 miles. It was pretty beat up wen I replaced it! Same headset in my racing bike was usable for less than 6000 miles.
Try parking a bike you like against a wall. Park this bike beside leaning on it so the handlebar tops line up. Step back and look at the two. Steeper fork? More fork rake? Could well be the answer. A fork with less rake (or having a framebuilder straightening a steel fork a little will slow the steering. (Probably need a paint job after. Straightening a fork is bending cold hard steel. Not a gentle operation. But it is how that fork got raked n the first place.)
Ben
Last edited by 79pmooney; 06-07-20 at 01:02 PM.