Digital BW, The Print

Do any of you have any idea why an Epson 2200 would very suddenly (but  
consistenly, now) almost completely stop printing one or more "colors"  
part way through something like an 11x17 print?

I can begin with a perfect nozzle check and full cartridges, start  
printing something that requires a fairly large about of ink, and have  
one or more inks essentially stop printing half way across the page.   
Grrrrr.

A nozzle check immediately after this happens looks like a disaster  
for all of the colors. A few hours later, usually after unsuccessfully  
running a couple cleaning cycles, it will be back to good nozzle checks.

It is *not* always the same cartridge.

It *acts* as though some kind of ink pump cannot keep up, or there is  
a leak in a line somewhere...  but I don't know how those Epson heads  
"suck" ink from the cartridges and "blow" it onto the paper.

Have any of you torn one of these things far enough apart to know  
where the "impotence" might be found?

I would probably just stop using the printer, but my new R1800 is  
totally useless for printing on canvas (something the 2200 does quite  
easily, I might add).

Thanks.
Myron