... type: single cylinder, air-cooled, 4-stroke 3) Bore x stroke: 39.0 x 41.4mm 4) Displ Specifications:Model: 139QMB (for 50cc ... )Engine type: single cylinder, air-cooled, 4-strokeBore x stroke: 39.0 x 41.4mmDisplacement: 49.5ccCompression ratio: 10.5:1Max. power ... : 2.0kW/7,000rpmMax. torque: 3.1N.m/6,500rpmStart: electric ...