I had a really worn out 2011 Agility 50. No compression. Cleaned the head, lapped the valves, new el cheapo rings and round (not flat-sided) rollers. Scoot did 29mph. Installed a generic 47mm BBK from Parts for Scooters and got 34mph. Rode it a few hundred trouble-free miles and sold it. Too beat up to sink any more money into. Learned enough that I'd like to do it again on a nicer Agility and go with quality BBK.