Re: Motorized Bike Lurching a Bit
These engines are not exactly torque monsters, so when not at the top of high rpm torque curve they will buck a bit. Always happens when breaking them in, but will get better with time.
It's also a matter of plug selection (NGK B5HS and do the wire upgrade), fuel control, fuel oil mixture (IE tuning)
Not sure what part of the country you are from, but when cold the problem is exacerbated. Mine takes farting forever to get warm when ambient is at 50°F or below.