Digital BW, The Print

I'm evaluating MIS UT-FS and UT-FSN inks for my Epson 1160, with both Eboni 
and Photo blacks.  Last night, I derived a curve (based on Paul's) for 
Ilford Smooth Gloss, using the photo black and FSN combo, and got really 
good results.  This morning, I've changed to the Eboni black to test some 
matt papers.

The nozzle check first thing was fine.  When I changed the black cart, I 
got initially nothing from the black nozzles so ran a cleaning cycle.  This 
got the black working (bar one nozzle) but killed the colour position 
(especially Y).  Running another cleaning cycle resulted in half the black 
nozzles going, and a few of the previously blocked colour ones coming back 
only for some others to go!

I've tried printing the purge pattern to no avail.  Why should running a 
head clean cause previously OK nozzles to "block"?  Right now I'm unable to 
proceed because I can't get a 100% nozzle check.  Does anyone have any 
suggestions please?

Thanks
Richard