Carburetor (CV, 18mm, w/ Accelerator Pump); QMB139 This is a high quality 18mm CVK replacement carburetor for all GY6 4-stroke 139QMB 49/50cc Chinese engines. This carburetor is fitted with a #85 main jet. This is better than stock and comes with a larger venturi, an accelerator pump, and quality construction. This carburetor is used on Baja, JMstar, Jonway, Lance, NST, Peace, Roketa, Sunl, Tank, TNG, Vento, VIP and many others. Mechanic Note: This is better than the stock carburetor comes with an accelerator pump, which will frequently eliminat e hesitation when you open her up.