I tired a fixed orifice and opened it up a few times before ending and giving up at 0.110 and trying the 178. It ran/idled better with the 178 and the fixed went to the used parts bin.

The Wagner in single stage is just an adjustable flow control valve. Looking at the Wagner parts, I am guessing that the Idle screw is a 10-24 set screw. The instructions indicate that 3 turns is the max opening, which should be about 0.126.