Ran across this SU Carburetor rundown on Facebook and it’s a great primer by Carl Heideman for Classic Motorsports:
Hot tip on tuning:
However, before the carbs are touched, ignition dwell and timing must first be correct. It’s a good idea to ensure valve clearances are correct as well. A quick check for vacuum leaks is next, and only once this is done is it time to move on to the carburetors.