I strongly suspect that your steerer is too long, or spacer stack too short. Possibly your star nut or expander plug is too high.
Whatever the reason, you cannot adjust the headset properly because the hardware is bottoming against the steerer before driving the stack down and loading the bearings.
Two easy tests.
1- apply brake and rock forward and back looking and feeling for movement at the lower bearing. Shouldn't be any. You can also do the bounce test, lift front wheel 6" and drop. should be silent, or the sound of a basketball bouncing. If you hear a clear "Clunk" your headset is loose.
2- leaving everything tight, remove the top cap and check that the top of the steerer is about 1-3mm below the top of the stack. (some top caps recess into the stack, and need added clearance).
Lastly, and don't be insulted because I have to ask, You do know that you cannot adjust a headset without first loosening the stem?
BTW- if it passes both tests and the headset is truly tight, you need to look beyond that. Possibly something loose in the fork blades, or the cables bouncing/chafing, and so on.
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FB
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