I recently rebuilt my 1979 Motobecane 50v and it ran terribly. I got that fixed with some help of another thread I made.
All the specific history of the bike and it's problems can be found here.
The last problem that's keeping me from riding seems to be in the variator. I had the variator circlips in the wrong order somehow and the porting was totally keeping it from making any power. I fixed both issues and now the rear wheel spins on the stand, I can rev the engine, and the engine variates. I have another problem, though. Despite working on the stand, if I put any weight on the rear wheel, no power is made to it. The engine will rev, the inner bell will spin, but it won't grab the outer bell.
Of note: I believe the variator is making the squealing sound you hear in the video and I was only able to put 1 0.8 mm shim between the first (internal) and second (external) circlips. I attached a video.
Upon the recommendation of pat splat I filmed a video detailing the assembly of my variator on the engine. I dissembled my variator (once again!) and made this video:
The last item I took off is on the left, the first on the right. The worn side of the clutch pads have about 2.5mm of material left. The groove on the stem of the external clutch bell is from it grinding against the case the first time I screwed up reassembly by reversing the order of the circlips (who needs a manual when you have a memory!). I also have a 0.5mm shim that is not in the variator.