Replying all the way into 2018. Oh well this is a very informative thread, hopefully there are still people following and active on this. On my current motorized project bike I'm having a huge pain in the ass starting the motor up if even at all. I have to use starting fluid :/. From what your post was saying I could drill out a brass plug that is in place of the A/F mixture screw. If I adjust the screw would that put life in the motor? I was also told that this motor might be running too lean thus it not starting up. Here's a picture of my bike: I have the HuaSheng 142F (49cc) motor. From recommendations from another forum I was told that there is a A/F adjustment screw hidden behind the brass plug on the other side of the carburetor. Pictured here: (A/F adjustment screw behind the brass plug closest the the engine) He stated "Lean engines burn cleaner, but too lean = no fire. I prefer slightly on the rich side, engine runs cooler." He said if I took out the plug, I would be able to tune the motor. Would this be the miracule cure to make the motor start?