I have a balance wheel & staff from a Wheeler which weighs in at 9.14 g.

I also have a Elgin, 18s 15j, grade 142 which weighs in at 9.36 g, a 22 g difference.

What sort of change would the lighter combination make?

I would imagine it would cause watch to run fast unless I am totally confused

The Balance Wheel oscillates at a frequency governed by the Hairspring stiffness. So if a particular hairspring allows a certain cyclic rate/minute of rotation for the wheel, a lighter wheel on that same hairspring will allow a higher cyclic rate/minute of the wheel and the watch will appear to gain time with that wheel over the heavier one.

Thanks to you both.
I figured it would gain. I just thought it would take more than 22 g or the weight of some balance wheel screws.