Here is something on which to ponder--
check both pistons on twins --
are they absolutely identical in color? buildup ? plug appearance?
The fuel mix they each see is the same --so why the difference?
How about cooling differences ( cowl shape )
internal flow ( mfgrs design)
different plug settings-your/someone elses setup -
mufflers?
pipes -differences?
Now then-- If you don't see any differences -- what engine are you running?
If you do see differences - how would YOU balance the cylinders?
and please no " buy a XXXXX engine they rock -sweet !"