Chris

What’s the problem with the large black cartridge and how have you come to this conclusion?

The large black cartridge has a lower quality ink used for black text, while the smaller one is a higher quality ink used for colour, mostly graphics and photos. But if you’ve replaced all the cartridges and you’re seeing the same problems then it is unlikely to be one of the cartridges that’s the issue.

Canon printers don’t integrate the print head into the ink cartridge as some do. The print head is a permanent fixture of the printer but it does wear out, and as it does it becomes prone to clogging up. You can eke a little more life out of the head by removing it and gently flushing it with clear warm water (no detergent) then allowing it to dry fully before re-seating it. But this only delays the problem. You can buy a new head but they are so expensive it is usually worthwhile to just buy an entire new printer.