Dan: You're asking how to get your particular glue to spray out of your particular guns, and that's hard for the rest of us to troubleshoot over the internet. When you say you're having trouble spraying the glue, does that mean no glue comes out of the guns at all? Or does that mean it comes out but not the way you think it should look? You need a fluid nozzle of from 1.7 mm to 2.2 mm to spray contact cement properly.
I would not thin your glue until somebody from Helmetin told me it was O.K. You said before you couldn't get the glue to atomize like paint, but contact cement is not going to come out looking smooth like paint, it's going to have a pebble effect. Are you sure the glue you bought is a spray grade? Helmetin makes spray grades of auto trim adhesive. Go to a place that fabricates countertops to get an idea what the glue should look like after it's sprayed, and ask them about the equipment they use to spray it. Good luck. Dan