Lectrons are the difference between "Running Just Fine" and "Running Like a Raped Ape!"
They are a Flat Slide Carburator, for serious performance machines. Very tuneable, can add powerjets, and have very strong throttle response. I'm running dual 34MM High Velocity Lectrons on my personal ride. Compared to any other carbs, they are night and day in performance. The XR750 Harley's always ran Lectrons on the race bikes, as do many other racing teams.
As a note, you CANNOT run filters on these carbs, they just pull too much air, and filters make them run so rich you can't stand it. For comparison, the intake bell (also a built in velocity stack) is 70MM OD for a 34MM Carb. A stock XS carb has a 54MM bell..