About changing to a smaller countershaft sprocket . . .
Chains don't like to change direction suddenly. Small sprockets put more
friction, wear, and tear into the situation. I suggest that instead of a smaller
countershaft sprocket, you consider using a larger rear sprocket. This will
not only help on rear wheel horsepower (compared to a smaller front sprocket),
but provide you the opportunity to take advantage of smaller increments of
ratio change (per tooth difference), thereby allowing more precise "tuning" .