Your black seems to have a lot of nozzles misfires,you cannot see it on the nozzle check on the normal mode, you check it on the diagnosis mode.
1. Before pressing the power on the up,down and right key,press it until the initializing is finished.
2. Use the left and right arrow key to navigate,look for adjustment menu.
3. Press enter then look for nozzle print.
You will see the full print of the cmyk,my solution to that is you need to ink charge your printer.but you have to be careful and extra cautious,too much inkcharge can break you printhead.
By the way how long you have using you mutoh?