Lexmark 1200 series refilling cartridge problem?

Hi,

I was few up paying expensive for new black cartridges so i bought a black ink refill kit from Maplin. I followed all the instructions as directed for my printer. Firstly, it was as if the ink had dried up so i added more, this worked fine for the first few days. Then when i went back to it it wouldn't print at all, so i took all the ink out of the cartridge with the syringe and put it back in extremely slowly and tapped it to make sure there were no airbubbbles in the cartridge, this worked but the next day it was back to not printing at all.

Could anyone tell me how to fix this problem or am i going to have to go back to paying like £20 for each cartridge? Thanks!