What could be causing a weird “rev hang”

I’m trying to dial in some dual Mikuni VM34s I got for my 750 that got messed with and aren’t in tune anymore. I’m not experienced with carburetors but I’m trying to teach myself. I got it to the point it idles well and responds well to throttle (in neutral at least) but for some reason it will periodically get seemingly stuck at roughly 4k rpm and I have to either blip the throttle a couple of times or briefly hit the kill switch for it to return to idle.

It has a new throttle cable and it doesn’t seem like it’s pinched anywhere so I can’t figure out what is wrong. I read that it could be a vacuum leak but I haven’t been able to find one.

What should I look for or check next?