Hi there, terryb
I went through these symptoms. I realized that tappets weren't set evenly. That didn't fix it, but then realized I had a difference of 5 degrees in my ignition timing, between cylinders. I did run one hotter plug on one side, and I also timed it at the mid-point between cylinders. However, upon my top-end rebuild in 2017 I go the same symptoms. Our engineer had, by then, refaced the magneto cam - so it was exactly the same timing, both sides. There was no other explanation but the classic induction bias - which is now fixed by Cake Street Classic's anti-bias gasket...