5k Aisan carb question - vacuum bypass?

OK lads, 

After fussing with my old and crusty Aisan for nearly a week, I threw in the towel after realizing gas was leaking out the main shafts.  A few days later, and I have a nice and shiny Chinese copy sitting on the wife's kitchen table.  Ahh, but it looks like some changes occurred in the design.  

- Top cover of new carb had the fuel inlet clocked 90 degrees the wrong way, and a different thread size for the central air inlet stem bolt.  To save aggravation, I just swapped in my old top cover (painted black because ugly).   

- Circled in green here looks to be a bimetallic switch which is controlling vacuum by some preset temperature.  This feature wasn't on the old carbie.  It's connected from the top of the inlet to the bottom throttle body port.  Why?

- Related to this is the two upside-down screws in the throttle plate, which are now standard screws on the newer design.  The old carbie had the pass-thru port in one of the screws, presumably serving a similar function to the new switch design.  

I guess I want to understand this bypass function a little better,  and learn if the new switch is an improvement over the hollow screw.