--Finally took one of my solenoid valves apart today and had a look at the individual components within. Then I had a talk with an engineer at Parker to find out the effects I could expect if I remachine one a bit. Taking the valve apart it's apparent that the greatest restriction is a tiny hole, maybe 1/16" dia that seats a pointed plunger. The plunger is the thing that's pulled up by the solenoid. After some discussion I've decided that the thing to do is to drill out the orifice a bit, increase the diameter of the moving slug pointy thing, increase the diameter of the sleeve it slides in, increase the dia of the spring that returns it to its seat, put it all together and see what happens. The goal is to lower the manifold pressure to maybe 40psi, which would make the use of propane much easier to engineer and which would make the air compressor less of a nuisance at events like Maker Faire.
--Plan B is to get a new valve. They've got 'em with as much as 1/4" bore thru with a 1/4" pipe connection which would connect to my existing manifold without modification, but they cost $40.- apiece. I want to avoid the 'more money' scenario if I can, heh.