There was an article in one of the RCmagazines in the last 5 years on balancing an engine. For the life of me, I can't remember which magazine it was or even the approximate date. I subscribed to MAN, Model Avaiation, FlyRC and RCModel World. I'm sure it was one of the first three though and if it was over two years back, it was one of the first two.

If I remember correctly, the blanceing didn't yield any more power, but did result in a little less vibes.

Don