Rev hangs after high rpm?

Hello, I’m wondering if anyone can help me.

My derbi senda has started to Rev hang after I WOT.

It happens when my clutch is pulled in, like I’ll hit the power band hold it for a few seconds and then pull the clutch in and the revs hang. It doesn’t do this with low RPMs though.

Was wondering if it’s carb related or an air leak, as when I first start in the morning the bike high revs from cold (around 4K and then drops) and the idles quite rough.