What rafter is saying is, the 4 petal intake of a polini will not flow all of a 24mm carb. You might still gain some power, but you arent making the most of the carb because your intake wont flow enough.
Some french 50cc bikes run up to 30mm carbs, but you have to have a reed block big enough to flow that (cr80 sized) and they have bikes with clutches and pipes made to work together in a very specific powerband. If you engine is tuned to make the grunt of its power between say 9k-12k rpm, and you have a clutch that can grab at 8.5k then a huge carb can work, but if you have a puch and your clutch is grabbing at 4k rpm, but your bike starts making power at 8k rpm, well I dont see a huge carb helping at all, probably just making your low end shit.
Atleast thats how I would see it. I know a lot of this years polini cup bikes will be running 28mm carbs.