This bike somehow landed in my friend's landlord's lap, and then into mine. The BB1 is a one-speed, Peugeot 102-style motor (but with a more vertical top end). I replaced the Gurtner with a cable choke 15.15 SHA, derusted tank & wheels, new Hutchinson 19 x 2.00 tires, repacked the wheel bearings, opened the intake to 15mm, and fixed the lights. Without trying to ruin the original aesthetic, or ruin any original parts, upgrades include: 50cc Peugeot 102 Parmakit (essentially a stock replacement with opened up intake and exhaust), a lighter Peugeot pulley, and an off-brand mini-circuit pipe.