I would like to add one more thing to Don's good advice. Whenever I buy an "electric" APC prop, I get this little piece of paper in the bag with the prop explaining that the small hole through the hub is a non-precision hole, and the larger hole on the other side of the hub is the precision surface. I find it impossible to balance my electric props, as the cones from my balancer have to engage both surfaces (one on each side). Although I don't recall ever seeing this explained when buying a prop for a glow engine, I am highly suspicious that this might be the case as well. In short, this might be an explaination for your (and anyone elses) problems with trying to achieve a proper balance on a prop with an off center hole.

Lm