It sounds like carb synching if it happens in summer and winter. Your bike should idle without wavering with the choke off.
I don't know how to do carb sycnhing, I guess I need some specific tools to do that right ? OTOH, my bikes idle okay, just when I riding in, let say, 2nd gear with 8K RPM, and slow down to 4K and go back up, the bike hestitate/choke a little bit, if I pull the clutch in a tiny bit it will help smooth it out. I'm not sure if it's a problem or was it just need to be downshift.