I don't know. Honestly, I don't see what harm could be done by taking some emery paper to the piston crowns. They should clean up nicely.
But be aware that it will take a few runtime hours to establish a pattern.
I don't think you can use piston wash as an immediate carb tuning tool.
Personally, I tune carbs by obtaining best idle speed, then observing off idle throttle response and picking the best low speed jet(s) for this. (I.e., the sequential order that Mikuni suggests)