Scooter intake manifold for 50cc 139QMB engines If your Chinese built 50cc scooter is hard to start or running lean, it may be time for a new intake manifold 30 Day Warranty Description Scooter intake manifold for 50cc 139QMB engines. If your Chinese built 50cc scooter is hard to start or running lean, it may be time for a new intake manifold. Note that this 50cc intake manifold model is smaller than the 150cc version. Please check the dimensions on the Specs tab to see if this is the right intake manifold for your 50cc 139QMB engine. Specifications Center to Center Mounting Hole Distance: 45 mm Intake Cylinder Head Width: 18 mm Carburetor End Width (Inside Diameter): 24 mm