I went for a short ride today as my 45 was looking a little bit dusty and forlorn. I've been focused on other projects so I thought I'd clear the cobwebs from it. It does have extensive modifications. Perhaps I'd forgotten or I've become too picky but I recollect it being smoother at speed. Perhaps the trouble is that I tend to compare it to my modern scoot which is dead smooth at speed. I jacked it up after the ride and checked the front and rear wheels for concentricity, free rolling and balance as best I could. The front wheel was like a perpetual motion machine it just didn't want stop spinning. The sprockets seem fine (none are hooked) and the chain is not stretched. It has a belt drive primary. The springer rockers are in excellent condition and its fitted with a shocker. Engine balance factor? Don't know as the engine had an extensive bottom end rebuilt when I purchased it many moons ago.
So how smooth is your 45?