Take a paper clip or other similar sized bit of metal. Put in airflow hole on side of base. Turn the adjustable center pin until the paper clip moves when it lines up with the hole in the center pin. Typically it lines up when the slot in the 510 connector lines up with the airflow adjustment screw. Should fix the whistle.
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Many Kayfuns can't have their center pin adjusted because it loosens the positive block on the deck. I can't even think about turning the pins on my EHPro KFL+ v2 because as soon as starts to turn the positive block starts to turn.