| the best way of balancing these 2 stroke cranks is to remove the same weight from the crankshaft as the piston weighs. say if your piston weighs 30 grams, you need to remove 30 grams of material from the crank circles, the area for this is located as close as possible to the cranks rod pin [ big end ] and as close to the outer circles as possible. when machining / drilling you must go through both left and right circle sides ie; 4 holes. if you want to keep internal case volume down you can also plug these holes with compressed cork, many guys use reson but i don,t trust anything hard that may come adrift in the case. going by this pic of the crank and piston i would say 8 mm holes would come very close to balance. | 
