With the standard Kit pulleys, a bit of skipping as you're describing is desireable. If you've got the results you're describing, I would put a small dot on the outside of the belt tunnel with a Sharpie to mark the adjuster screw position and leave it alone. Sounds like a dream, especially if it's fast.
To make sure there is no confusion, spur gear sizes are as follows:
100 = black (obsolete)
102 = white
104 = black
106 = white
108 = black
110 = white
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