holley carb question.

Looks like a Holley 1920 metering block. That is the part that you can't easily dissasemble and probably gets fouled, and why so many bad rebuilt ones are in the pipeline. I recall some posts on how to reverse blow the air ports to clean them.

The brown lever is part of the "economizer", as I recall. I think it actually serves to enrich the mixture at higher speeds, similar to the "power valve" in the bigger 4 bbl Holley's. It is activated by a vacuum piston. Your's has a 2-step enrichment normally, but only 1 step with the broken finger. I don't think it would be active at idle so probably doesn't explain your problem, which I expect is a "too lean" idle where it slows way down and shakes when you shift to D. That plagued me for decades thru several 1920's until I got a good one.