These kits (I got mine from ScrappyDog) are really awesome. The starting & acceleration is really impressive, although the top speed doesn't change much. I also added a performance CDI to increase max RPM, and a set of hi-speed gears to increase top speed. The Kymco 50cc 4T SD10E seems to be a standard qmb139 engine, and every qmb139 part I've used fits exactly. I now cruise easily at 9,000rpm at 45mph (70km/hr). The only part needing some extra research are the reduction gears (one of the gear clusters is a Kymco piece, not a standard qmb139 piece. But it's easy to sort out). Another tip: the 80cc kit is a 60% increase in engine size, and the little battery struggled to twist the qmb139 starter. I upgraded to a 7-series battery and it now starts like a pistol shot! Other parts used: #90 carb jet; straight-thru sport muffler. Removed intake restrictor grommet, but kept stock air filter & box. Switched to 7gm variator weights, Honda Dio Keli variator with stock clutch. It's really loud now - and really quick!
