What type of fuel are you using?
A few months ago I was working on a Banshee for a friend of one of guys that to that rides in our group. It was experiencing the same symptoms that you are describing. I went completely over the banshee from compression test to leak down test and exchanged carbs, reeds and even all the electrical part from an excellent running banshee and the symptoms were still there. It drove me absolutely nuts. I even drained the fuel to see if it was contaminated. It looked fine and so I put it back in and it still had the same symptoms. I then again drained all the fuel out and I even flushed the tank out and put some of my own fresh 32:1 pre-mix and the symptoms went away. So I talked with the owner and asked him what type of fuel he was using and he told me that he was running VP T2 fuel and mixing his fuel @ 32:1. He didn’t know that VP T2 comes already mixed @ 40:1 from VP racing. So he was adding 32:1 to fuel that was already pre-mixed @ 40:1.
So the problem could be with your fuel that you are using. A lot of states start right around August to switch to winter blend fuel and fuel at your local gas stations are loaded ethanol which is not good for anything other than your car depending on the percentage of ethanol. I have everything I own from my 1987 Buick GNX all the way down to my weed whacker is on an ethanol free diet. In my area I can get ethanol free 95 octane Sunoco Optima at the pump locally.