Epson Stylus Colour 740 ink jets plugged or dried up (Black works)?

Hardly ever use this printer. (maybe once every 4-5 months) Not printing in colour and the ink level indicator shows all colours are full. Just purchased a new black cartridge and works well with black type, but if I print a colour page like a map, the black type on the colours (street names etc.) are all washed out, but the headings etc. are very crisp black. I have saturated the bottom of the ink cartridge colours and the needles that the cartridge sits on, with alcohol, but this didn't seem to make the colours work. Don't want to take in for service because it would probably cost more than a new printer. Anyone else have this problem?