Digital BW, The Print

I'm using UT-1 inks on an Epson 2100.

I have a strange problem that I wonder if anyone else has 
experienced. I've refilled original Epson cartridges with the MIS 
inkset using the standard technique described on that very exhaustive 
website with all the colour pictures (don't have the link now). 
Afterwards, 6 of the 7 cartridges gave perfect nozzle checks with one 
cartridge (the light magenta position) refusing to lay down any ink 
at all. Head cleanings don't help, but uncrimping the filling tube 
and sucking out a little ink through the exit port using the bottom 
fill adapter followed by re-crimping the filling tube typically gives 
me a perfect nozzle check on this cartridge. After that I can print 
one, maybe two large prints before the nozzle check reverts to no ink 
being laid down again.

When I replace this cartridge with an original Epson cartridge that 
hasn't been refilled the nozzle checks are fine, and stay fine, so 
the problem is with the cartridge. I've since prepared a second light 
magenta cartridge for refilling and have the identical problem - it's 
either perfect nozzle checks or no ink being laid down at all from 
that particular cartridge.

My feeling is that it is almost like there is a vacuum within the 
cartridge that is holding back the ink and not allowing it to be laid 
down. I say this because when I introduce the bottom fill adapter 
when the cartridge is not laying ink down I initially feel a slight 
resistance when pulling back the syringe, and I draw out air from the 
cartridge, followed by a 'letting go' after which I get an ink stream 
re-established. As I say, after doing this the cartridge works fine, 
at least for a while, after which another air pocket or some kind of 
vacuum seems to form.

It just seems a bit odd to me that I've had this problem with two 
light magenta cartridges now.........has anyone else had anything 
similar? I guess I'll just prepare a third but wanted to report here 
and see if anyone had ideas.

Best regards,

Dave