I don`t often divert off the plans that often but I was having real problems with back stop and I figured it was all down to its position. The plans call for the backstop to be mounted alongside the count wheel on the bridge piece as I originally built it:

However the angle at which the backstop engages when in this position is not at all ideal as it bears down heavily on the wheel and it also doesn`t slide over the teeth as easily as it would if it was more horizontal or more parallel with the tooth flats, similar to the position of the opposite gathering pawl.

I therefore made a new mounting bracket fitted from the bridge screwing point and the screw at the back is a counter balance, the nut allows more fine adjustment of this. This really reduces friction on the count wheel. I made this modification much earlier on with an ugly temporary backstop that you may have seen in the videos of the running clock. I would certainly recommend this modification: