I have done the crank weight adjustment and did the original posting. The 75% # came from george Claussen or go fast George, cant remember which. This is a reference point used by most engine builedrs to achieve a ballance point in the upper range in the rpm band of a kt or 2stroke engine running around 12,000- 14,500 . I installed a 54.5mm Ausie piston in my kt that weighed 28grahms more than a 52.70 piston. I installed two 3/8 by 1/2 tungsten weights at 14 grahms each. These were 180 degrees from the wrist pin the location the same distance in on the wheels as the wrist pin one in each wheel. The steel removed from the holes in the wheels weighed around 5 grahms to 5-1/4 grahms,that equals 10-1/2 grams. The tungsten weights were 14 grams each or one ounce 28 minus 10.5 equals 17.5grahms of added weight or about 75% of the added piston weight. This worked extremly well for my kt it balanced it out very well in the upper range. I was vibrating so bad before doing this that my engine was throwing the anti-vibrating rubbers in the head and cylinder. It also seems to have increased the acceralition, but i installed a new pipe and carb which may account for some of this feel. Never had a chance to dyno this build or race it much becuse I been on the road with my job, havent even been on bobs in a long time. You could experiment with the 75%# and maybe increase it if you plan on running a higher rpm or even to see where it moves the balance point but Iam very happy with mine. Do not use lead it is to soft and doesnt have near the weight difference as the tungsten. I bored the holes about .004 undersize and heated the crank to about 450F and froze the tungsten dowels in liquid nitrogen and they almost fell in. I also bored them about .010deeper than the dowel length and fit them flush to the outside of the flywheel. Good luck hope this helps