I guess if the JS provides an unnecessary reduction but how I first read it was that he flipped the sprocket to the inboard side and it picked up. How would flipping it eliminate the jackshaft unless it reduced too much and wasn't needed.
Correct. I flipped the clutch moving the sprocket from inboard to outboard thereby allowing a new chain to be made that ran directly from the clutch to the rear sprocket effectively eliminating the two inner sprockets that were part of the original jackshaft that was geared as a reducer. A spacer had to be made, and I had to drill a hole in the middle of the crankshaft for a bolt to hold the clutch on because the original snap ring doing that job would not line up.