I got to the mystery diaphragm yesterday. It has a screw through the middle of it that acts as a linkage pivot point for what appears to be a bowl vent. The diaprhragm itself was not only as hard as a rock but the screws on the cover were loose. As a result, gunk had found it's way inside of it and clogged up vacuum galleries. If the Lancia this carb came off was still running, I'd imagine it wasn't running nicely. I'm about to take the big step and pull all of the throttle shafts and butterflies out of this sucker as it will be the only way I'll be able to give it the thorough clean it needs before properly installing the rebuild kit. Man, there are a ton of springs, linkages and shims in there. Nothing like the Mikuni...