Trigger: I hope you're right - that I have a clog in the magenta cartridge or magenta print head nozzle. I can probably fix that.
Here's what I've done: To avoid immersing the print head in water, I put a snug-fitting clear plastic tube over the print head inlet after removing the rubber gasket. Using a 10ML syringe that fit snugly into the tube, I slowly injected Windex into/through the print head forcing the ink out into a shallow container. When it flowed clear, I placed the print head on a four layer fold of paper towel and filled the plastic tube with Windex. It wicked into the paper towel in less than 2 minutes. I filled the tube 3 times and it flowed freely while I waited. I did this to the yellow and magenta inlets only because the black and cyan seemed to be OK. I removed the rubber gaskets around the color inlets and examined them under a magnifying glass. They are pliable and appear smooth with no cracks or distortions. I shifted them one color position when I re-installed them.
The cartridges were already fitted with silicone rubber plugs. I flushed the BCI-3 yellow and magenta cartridges with hot water using a 16 oz. squeeze bottle with a tapered nozzle. I blew the cartridges as dry as I could by mouth. I then filled them with fresh Hobbicolor ink. Before putting them in the printer, at your suggestion, a gentle puff over the vent hole ejected a couple of large drops into the sink.
I installed the print head and cartridges in the Canon i850 printer and then did one deep cleaning and a couple of regular cleanings of both black and color. I did a nozzle check. I printed a four color bar chart using plain paper and standard quality preference settings. The first bar chart printing was at 10:25 AM, the second bar chart a half hour later.
The accompanying graphics show my print head cleaning method and the nozzle check. The first color bar is OK, the second has banding in the yellow. I scanned the nozzle check at 400 DPI, cropped the image and enhanced the colors. The yellow is not as clear as it should be but there doesn't appear to be any yellow nozzles missing. After a cleaning and a good bar chart print out, the second bar chart print out a half hour later shows the yellow starts with an orange hue which progressively diminishes to just banding stripes and then is almost clear yellow at the end. Three hours later I did the same color bar print out. The yellow bar was a solid orange at the top diminishing to shades of yellow interspersed with orange lines. The cyan was a lavender color. So it seems that within a half hour, without any activity, the yellow and sometimes another color takes on an unwanted hue. The results are the same with a solid yellow purge pattern.
Just for giggles, I put the suspected print head back in its original home, the Canon i560 printer. I installed the original i560 BCI-6 cartridges. After turning it on, the printer went through its thing which I assume to be a cleaning cycle. I then launched a service mode nozzle check. It looked OK. I returned to the normal mode and launched a color bar print out. The color bar looked perfect. After 35 minutes I did a second color bar print out. Now it displays the same orange banding in the yellow bar and this time there are white lines in the cyan bar. The magenta appears normal.
My speculation is that the yellow ink (and possibly others) is being contaminated within the print head by a slow internal bleed from another ink channel. When purged by a cleaning cycle or a four color bar chart print out, the yellow begins to clear up as fresh ink replaces the contaminated ink.
