If you are looking for the best bang for your buck in performance on your GY6 motor this is the kit. The 171cc (61mm) big bore kit is the largest big bore kit you can go on the GY6 A motor (Chinese GY6 qmj157). Like they say “There is no replacement for displacement “. If you want to add the performance cylinder head (click here). For the money this kit flat out rocks! We even have a install video! We would recommend adding a cam shaft (click here). You can even add a performance carburetor, but it’s not a necessity. (Click here)
You may find other kits for half the price online but note they are made in China. This kit is made in Taiwan and there is a HUGE difference in quality.