I had this problem on one of my bikes... I had the clutch cable & CDI wires zip tied to the frame, & when I pulled the lever it was messing with the wires.
Cut off the plug ins & solder & heat shrink the wires!
I know this sounds like a simple fix and please don't take offence but have you tried turning the idle screw in a little? In= higher idle speed, out= lower. The idle screw is the one with the spring and screwdriver slot on the left side of your carburetor. It engages the throttle slide and allows or prevents movement past a certain point depending on how far it is screwed in.
Tom