I make only infrequent use of my Canon Multipass printer, sometimes letting it stand idle for several weeks.  For whatever reason, the black ink tanks clog the printhead after prolonged disuse whereas the color ones keep functioning.  Although more likely to happen with a clone, the same has occurred with Canon originals.  Before throwing out the printer (and I've come close), run it through the cleaning cycle at least 5 successive times and try printing again. If it's still not working right, do another 5 cleaning cycles.  So far, that's done the trick for me, but if 10 times doesn't produce the desired result, you'll need to do some invasive surgery on the printhead itself.