Digital BW, The Print

Mark,
your struggles are familiar (with 1160,1270,1290 printers). AFAIK it
is really important not to do more than 3 clean cycles without 
stopping for a rest (for the printer) and (very important) then do a
small print
(purge pattern). 
The "cleans" are not all the same (short, medium and long), and I
think the pattern requires to be reset after a set of 3 to work well. 
Look for the cause of the problem - if a couple of sets of cleans do
not fix it. There are many resources with advice (the old mwords.co.uk
pages, MIS, etc. etc.), but thoughtful diagnosis is the best way to a
cure.

Ken