According to this your '75 is different than my '77.  Yours should have a screwdriver adjustment not a nut like mine.  @Captain Obvious has a good post about 60% down the first page.  Let me try the new way to get there...

 

Here's 76.  Whatever you're turning, it shouldn't be loose.

Here's what the nut looks like. I can't turn it with my hand but it will plunge into the body of the BCDD with some resistance. It feels spring loaded or like pushing against air pressure. When I let up, it returns to the down position.

Got some under hood time with the BCDD. With key in on position and touching solenoid wire to connector it would click. With car running and wire disconnected, car would idle up at ~2k rpm. Hook the wire back up and it would settle back down to 800rpm. Turning the screw on bottom of BCDD had no effect on the high idle when solenoid wire was disconnected.

Took it for a drive and the rpms would stay up when shifting and coasting, worse than before. I could pull up the pedal from underneath and it would drop, but pretty hard to drive that way. I thought I was going to have to take the TB off and clean it but when I took the linkage off it, it seemed to slam close pretty good disconnected from all throttle linkage. I checked the throttle linkage and found the FPR rubbing on the linkage. What a pain getting that to move enough for it not to rub. I cleaned up the linkage, and the balls and greased them. Low and behold, rpms drop now when letting off gas to shift.

I don't know if the BCDD works or not, but it's driveable now. Also discovered I don't have dash pot on TB either. 

Siteunseen. I routed my PCV hoses like you did yours. Pretty cool, got rid of a small metal tube with bracket and about 4 hose clamps. Also discovered I still had the flame arrestor in my original hose. Thanks for that.