Al,
The more agressive taper on the TBS needles seems to cure a slight stumble or flat spot at midrange rpms for most of us. However, most of us (as far as I know) never used shims on the stock needles. By using shims on the shorter stock needles, you were probably achieving the same result where the jets flow's overlap at midrange.
Look on the bright side. For $16.00 you have 4 less pieces in your carbs to deal with and that much less weight to haul around!
