Engine running erratically or not wanting to stay at idle? It could be your intake manifold boot. The rubber gets a crack in it allowing air to enter without picking up fuel at the carb. This fits all GY6 139qmb 4strokes. Tank, Sunl, Roketa, Vento, TNG, VIP, Baja, Jonway, JMstar, Peace, Lance, NST, as well as others. GY6 139QMB. Easy 2 bolt installation and vacuum line nipple.