Digital BW, The Print

I suggest that your clogs are really trapped air at the discharge port
-in my experience with my 4 Epsons that is what is happening. The
remedy is to make sure there is little or no air right at the  ports
when you put the carts in and the best way to do that, I have found, 
is to vacuum fill, if the cart is an empty, or to suck quantities of
ink  through the cart via a syringe and exit port adaptor (MIS
supplies them or  break the tip off a large needle - the plastic part
of the needle should fit the port seal  well). 

When you've pulled enough ink through the cart to eliminate the foam 
with the cart *held upside-down*, 20 - 30ccs usually does it,
carefully  raise or lower the upside-down cart in relation to the
reservoir so that you  see the ink level come right up to the port,
pushing out all the air (a  bubble may form - be careful not to get
inks contaminated with one another).  Now you can either clamp the
tube so the ink can't drain or quickly, in one  swift move, put the
cart into the holder (you might want to practice the  move with a
closed cart so that all the tubes and the head are right where  you
want it and nothing gets in the way.) 

If you're doing this without the  clamp and it takes more an a couple
of seconds to put the cart in for any  reason - do it over again from
the point where the ink is visible at the port with the cart
upside-down.  I have been doing my cart installations this way for
almost 3 years and  since then have had none of the headaches due to
so-called "clogs", which I think  really is trapped air that the heads
can't suck out. Besides that, I can  almost always start printing
immediately or with at most an hour's wait; my  first or second nozzle
check is perfect.  

Finally, the last thing is to make sure that your tubes really are
down to the bottoms of the reservoirs. I know it seems obvious, but I
just had this happen and I was intermittantly plagued by what seemed
like an air leak in the yellow cart. Somehow the tube had worked out
and up to the ink level and was sucking air/ink mix and that
eventually worked it's way down to the port.

Good luck,  

Frank

PS: I have an extra tube taped to my ribbon tubes for an optional
black cart and there has been no problems - the tape locations have to
be carefully checked by moving the head across the track manually a
couple of times and keeping an eye on it at start-up, lest the tubes
hit the drive belt and possibly jam.