The x900 and x890 seem to be more prone to clogging and flow issues than previous models (no matter what ink is used).
After reviewing your order history, I see you bought a set of 4900 refill carts with Special Edition K7 ink in February, then five more individual refill carts and Warm-Neutral K7 ink earlier this month. Please explain- are you using one 4900, and making your own custom ink set, or switching this 4900 from Special Edition to Warm-Neutral?
What position(s) are you experiencing clogging in?
When did this clogging begin?
What happened before the clogging began- were any carts removed, refilled, new carts installed, printer sat unused for a while, printer was used frequently, etc...?
How frequently are you experiencing clogging?
How often have you been agitating the ink cartridges?
About how many nozzles are generally missing, and how quickly/easily do the nozzles return?
How often do you use the printer vs. how long does it sit unused?
What are the temperature and humidity levels in your printing environment?
You can find some general printer maintenance/cleaning information here: http://www.inkjetmall.com/tech/content.php?133-Printer-Cleaning-and-Preventative-Maintenance
Please let me know so I can try to help you get past this pesky issue, and back to happily printing.
Best regards~ Dana