Digital BW, The Print

Had posted a question earlier that I was not getting a good head 
check on the yellow position of my 1280 using Piezotone WN inks. Just 
printed a 21 step gray scale and the first 30% is all white no steps. 
I believe that I have a clog or they didn't load up the shade of gray 
that goes where the yellow head would spray. Since I have cleaned 
heads 20+ times what should I do? 

Any help would be appreciated.

Thanks,

Barry