Gary
I'm not sure about using a spray gun with a kirby, but I have used a professional automotive HVLP spray gun attached to an air compressor and I dilute the paint with low odor paint thinner. There isn't a set amount of thinner to use, normally I go based on the suggestions of the paint manufacturer, and most of the time, I'm doing like 50:50 on paint/thinner. Like I said, it may not be exactly the same process (I'm thinking this would be more like a Wagner Power Painter system), but it's not too hard to do. Hope that helps some.
P.S. I would recommend practicing on something old before you get too wild with the sprayer, the thinned paint has a tendenancy to run and can ruin your paint job rather quickly!