I had exactly the same problem. I tried cleaning the head, the cartridges, the tracking wheels (or whatever they call those metal shurikens that hold the paper onto the platen). Nothing seems to work.
I finally found out what was causing these specks. A small piece of fluff was stuck to the...
I've got an ip4200 already and interested in a CIS system. Do you sell the CIS kit?? Would you be able to supply the parts for me to DIY it with my current carts.