I built another bike last night using a 2011 48cc grubee. The first thing I noticed was the square cyld. head like the 66cc , longer clutch arm with a slight bend to tuck the arm in under the carb better. clutch cable boss is machined in the crankcase at a better angle. Also a redesigned exhaust port angle. I moved the e-clip on the needle to the bottom slot before installing the carb. It started right up! I noticed right off that this engine has much better mid range torque, also it seems that grubee has worked out the bugs in the cns carb because this one runs great! The only adjustment I made was lowering the idle. It sounds like someone is reading the complaints!