Grant,I too have seen this action you describe where a sudden return to idle resulted in a stall or near stall before returning to a normal idle.
I think it is because of a residual rich condition--the engine not being able to burn itself clean before going back to idle where less air is available-spark is retarded(ported vacuum)--and the idle mixture is leaning toward the rich side anyway.
In fact I have,rough and dirty,leaned the idle mixture as much as possible and increased the idle speed and advanced base timing,to live with this (should have made corrections to avoid an EXCESSIVELY rich mixture from accelerator pump and power circuit).
Have you ever used the accelerator pump adjustments provided by the linkage to increase or decrease the delivery?Also the power valve tuning can be manipulated to correct within it's field of operation.
These reactions of the engine to a particular carburetor are the reasons Jerry and others tell us of the problems of multiple carburetion where "non-matched" or standard carburetors are used.The original correct mixture management (jetting) provided for a single are not correct when a duplicate (hopefully) is sharing the duties.
I have seen these dashpot applications (can't remember where)to slow the return to idle I think mostly on auto trans cars of the years when the manuf was struggling to reduce measurable emissions.
Come to think of it our current electronic injected engines are modulated in return to idle speed by the computor/idle air controller for this same result.
