I'm fairly new to carbs, been playing around with them but never did understand the intricate details on how they actually work.  Found a neat youtube vid that explains how they work:

https://www.youtube.com/watch?v=toVfvRhWbj8 

 

Go to Youtube and search "University Motors SU Carb"  It's a fantastic series of videos on British  SU's.  95% of the information is exactly the same as our Datsun SU's.  

The high speed video of the transparent carb makes you wonder how carbs actually manage to work so well in the real-world, under-the-hood, driving on less than pristine roads! This was really fun to watch!