Anybody know anything about the carbs on a 500?

Got a brand new carb for this thing but there are no screws for adjusting anything except for one on the very bottom on the engine side of the carb. No idea what that actually adjusts, as it seems to make no difference at any position, all in, all out or anywhere in the middle.
It has a dead spot right off idle where it’ll actually die if you try to just feather the throttle up to about 20% or so. If you quickly go past that point off idle, it’ll run and rev up like it should but it also seems to have issues at close to max throttle. It only likes midrange.
It starts and idles fine.
FYI the machine is new to me and I got it from a guy who said it needed a carb. It seemed to have the same issues with the original carb as well which I figured a new one would remedy.