I'm a grad student teaching an intro course to religion at a big state school. When giving Big Test #2 (out of 3 for the course) to the first section, I noticed that it was taking even the better students far too long to complete the test and figured I'd made it too hard. So I cut out a chunk of the test for the other section.
The end result is that the average in Section II is 10 points higher than Section I, which I don't think is fair. (Also, in the case of Section II, the average ended up too high, at 89%.)
Next time, don't make such a drastic change to the exam between sections. This will allow you to adjust all of them. You could try just scaling the grades up for section I.
I suggest you go search the "In the Classroom" forum, also. There was a very involved discussion that covered adjusting/grades and reasons in favor and against it (I don't remember the title of the thread even though I posted in it).
Alan