Bitsyncmaster-thanks. My rest pressure with the FPG valve open is about 30. I can't get it anywhere near 50PSI running, but the engine won't idle, so i can't get it to run for too long. With the FPG valve closed, it jumps to about 44PSI.

It seems to me it's likely I have a vacuum issue, maybe? If so, where should I start investigating? Nothing changed at all upstream of the CPR, so I'd have to imagine the first place I should investigate is the mixture unit and fuel distribution unit?