50cc QMB139 4-stroke 50mm, Non Emissions（Non EGR） Cylinder Head with 64mm Valves for use with 81.3cc Big Bore Kit! Now you can customize 50cc QMB139 4 stroke big bore engine kits as you need. Then the components can be optional Bore Displacement: 39mm 44mm 47mm 50mm Cylinder Heads: 64mm-EGR 64MM-Non-EGR 69mm-EGR 69mm-Non-EGR Gaskets: Short Cvt Cover case Long CVT cover Case Mufflers: Varieties of Colors More please discover here.