I'm not an expert but I've learned a lot playing with my Scamp, it's carburetor, and the AFR gauge. But I think the way our carbs work is the cable turns a throttle valve open to allow more air. But the slide doesn't move 1:1 with the throttle. The slide works on engine side vacuum. When the engine pulls more air through the vacuum increases and the slide begins to rise. The slide in turn controls the maximum amount of air the engine can draw past it while simultaneously contolling how much fuel goes to the engine because that slide acting on vacuum is also pulling the jet needle up out of the main jet and (needle jet?). The AFR stays more constant due to this design.
My Scamp's Edelbrock carb doesn't work this way. The throttle valve just slams open, air is going in and unless the carb set up is proper, it will go lean. And it is very difficult to get it proper. My Scamp is tuned to perfection though and it still has conditions where it goes too lean.
So I'm anxious to get the AFR gauge on my rebel to see how accurate it holds the AFRs.
2016 Honda Rebel 250 - The "Piglet."
AFR sensor equipped and downsized to a 0.105" main jet.
The only changes so far.
Bought on 6/29/19 with 44 miles.