You might like to take a look at this youtube video on how to setup a HF purple gun.
This is not me or my video but I think it would be a good practice to prep any gun this way.
I got the HF gun mainly for primer as I'm not going to pay for a high-end gun to do a single DD project. I'm still getting used to shooting with it but I'm satisfied with the results so far. (Primer) I was going to rebuild my Binks #7 for the finish coats but may shoot them with the HF gun instead. I haven't shot a car since the sixties so everything has changed a bit.