Yep, time for a bag wash or replacement. If its original to the machine, id recommend replacement with a new bag, and save the old one for show.
First tho,before washing, after a thorough shaking out, vacuum the inside of the bag with another vacuum and crevice tool. I like to use an Electrolux or TriStar for this, as all of the dirt will then be easy to dispose of. I like to quickly turn on and then turn off the Kirby, just long enough to inflate the bag, shake the bag with the Emptor tray closed, then vacuum out the Emptor, close again, and repeat, until the dust stops falling into the Emptor.(you know you've gotten most of it by now)
Then entirely remove the Emtor and bag from the Kirby, and go over the inside of the bag thoroughly with the crevice tool,,then remove from the Emptor and take the top off, turn inside out, and wash by hand in cold water and Woolite, and let air dry. If the bag is extremely dirty, you may need to change the wash water once or twice,,and be sure to rinse thoroughly under running water. Also be sure to wash and rinse the Emptor itself, the bag guard, and make sure the seal around the Emptor tray and neck are present and tight.
Yes, you could have a new liner sewn in, but if its an original, i wouldnt.