The red things are velocity stacks, and their purpose is to manage the air entering the carb. Many design characteristics determine how they function.
A long velocity stack gives good low-end midrange performance, but hinders top-end somewhat. Conversely, a shorter velocity stack will give better high rpm performance, but won't deliver the goods in the midrange or low down.
Other factors concern the radius of the bell opening, length of the stacks for the center cylinders vs. the outer ones, etc.
The flatslide carbs are directly connected to the throttle cables, so when the rider whacks the throttle open, the slides go fully open. At high rpm, this is okay, but at mid and lower rpms, the engine will stumble & fall on its face because there isn't enough intake velocity generated by the engine to mix and atomize the fuel with the incoming air. Open the throttle slowly at low rpms, and all is fine. It takes practice & discipline to use them properly.
Flatslides can also be problematic to setup to fuel properly for street use. You're likely going to become very familiar with carb removal and installation while trying to get them to work how they should. If you like to tinker and relish a challenge, you're in luck with these jewels.
At full throttle, compared to a typical OE constant velocity carb the flatslide has only the needle obstructing the airway. A CV carb has the needle and throttle butterfly, which degrades airflow.
Hope this helps.
