Firstly you need to recognise the feeling of the ku ku ku then add each step.
Start with the aahooh and even say the ku aloud, then disengage the vocal cords, add tissue and visualiser (or fingers), mouthpiece then lead pipe.
You’ll soon discover which part of the process you are compromising when you are playing which is inhibiting the ku attack.
I suspect you haven’t yet got the sympathetic oscillation of the lip and thus dealing with too much air pressure in the mouth. I also think if you look closely (with your eyes closed) your throat might be closing. Have a DEEP look around the system.