Naraku Secondary / Final Drive Gears for 50cc 4-Stroke 139QMB Scooters COMPATIBILITY: BMS – Apache 50 4T, Heritage 50 4T Diamo – Classic 50 4T Lance – Charming 50 4T, GTR 50 4T Roketa – Bahama 50 4T, Maui 50 4T, Sicily 50 4T Tank – Urban 50 4T, Sporty 50 4T, Viaggio 50 4T Many Other 50cc 139QMB Based Engines **This will not work on the QJ models Who doesn’t know the feeling Performance tuning with a big bore cylinder your scooter??s acceleration increases significantly, but the top end speed is lacking. The variator brings a little something, but the top speed just is not enough. The reason for this lies in the original transmission so that the relatively weak original engine can achieve the desired power, the gearing is set too short. NARAKU offers a 10% taller gear, which achieves the optimal translation for 4-stroke engines. Minimum bore is at least a 47mm / 72cc cylinder kit. With the change of ratio, the scooter will now experience a significant increase in top speed without sacrificing acceleration. The NARAKU kit is easy to assemble and already pre-pressed. Simply swap over and you??re done! No special tools required. Fits all 50cc GY6 engines. The 10% ratio change applies to vehicles with stock gearing 52/16 and 51/15. In general, that accounts for 90% of Chinese 4-stroke models. Please check in advance which original transmission is used in your vehicle. Some TaoTao models already use the upgraded gear version so please verify this before placing the order. **