That is a strange one. Could be the famous chinese quality control. I see you're in Arizona so maybe your air filter is letting dust in there. If it's an older carb then maybe time to replace?
I have a brand new nt speed carb with a very sticky slide that I can only move by pushing with a chopstick. I can't figure out how to hone the slide chamber without wearing down the guide pin. I don't want to sand down the slide itself. I'm going to try the dremel with the plastic brush wheel. That's all I can think of.
This is assuming you have an NT carburetor. You didn't say.
If you overtighten the cap where the cable enters the carb it can distort the bore where the throttle barrel rides. That cap should be 'finger tight' only. Don't use a wrench or pliers to tighten it. Also the barrel only goes in correctly one way. If you have it reversed it will not move as it should and will bind.