Great description. I have a Roch B on my 216 that runs nearly flawlessly (knock on wood) so they do have that capability.

Without an air cleaner on it does make a pretty loud sucking sound down the throat. Cars of that era had special air cleaners that looked like oil baths but the large chambers were for muffling the sound of the carb drawing air. Just thought I'd add that to the convo.

re. fuel/air adjustment inop.
Sounds like the power piston(s) may be stuck in either the open or closed position. With little engine vacuum it's supposed to open and dump more fuel into the venturi (like when accelerating and/or the throttle is opened past idle/low speed to compensate for more engine load).
And at high vacuum (idle/low speed) it's supposed to close and not allow the additional fuel, allowing the idle/low speed circuit to fuel the engine).
I'm unsure what circuit the power pistons fuel travels as I've got Roch B's with differing internals but it could be rendering the idle circuit inop.


1949 Chevy 1/2-Ton 3100
1949 GMC 1/2-ton 100
In the Stovebolt Gallery
More pix on Photobucket
Video of the 216 running
Video of a Winter Cruise