Don’t need a big carb on a derbi, especially with the stock reed design. For that matter, stock av10, Peugeot, Puch Polini kits, hobbits and even tomos all run amazing with 15-19mm carbs. The stock reeds can’t flow much more than 19mm and while you can put a larger carb on, it kinda just ruins your gas mileage.
Reed valves also tend to smooth out one of the bigger issues with a sha. Like how if they’re tuned right for when the pipe hits and the top end of the rev range they generally will be rich in the bottom.
I don’t like performance of a sha that much, though it does still cruise at 50 no problem I feel like it could be smoother when I roll on from idle. I still don’t get the cutaway tuning.
I do however like not having to worry about running out of gas on group rides and never having to tune.