I think you really need to distinguish between drivetrain slack, and engine/carbs. Adjusting the chain won't fix an out of tune carb, and neither will the opposite. Rolling on and off the throttle will produce SOME drivetrain (chain) slack feelings, especially in the lower gears...Drive your car in 1st gear at around 10mph, then let off the gas, I guarantee you'll feel pulled forward out of your seat. The bike will feel the same way.
What you need to do is ride it at a steady speed (throttle position) and note any stumbling, missing, spitting, whatever, then go on to examine setups, jetting, air screws, etc...I'm afraid you're mixing apples with oranges, and confusing yourself...
