I've brought back a 1983 PA 50ii from the dead. But still not able to get it up over 15 mph. Bike runs great, but slow. When I give it full throttle I feel an intermittent surging. She feels like she wants to go, but something is holding her back. Replaced the roller weights up front as they were shredded. My next guess is that the culprit is the rear pulley. I've taken it apart and the interior looks pretty gnarly.
If that doesn't do the trick, what would you recommend next? CDI box? Carb?