CG250 (167FMM) Balance Shaft
I believe all CG250 (167FMM) have a balance shaft which is an eccentric weighted shaft which offsets vibrations in engine designs that are not inherently balanced like the one cylinder engines in the DF and the Heist.
The CG250 is a enlarged clone of the Honda CG125. The CG125 was designed by Honda in 1950 so it's not the latest and greatest in technology.
http://i182.photobucket.com/albums/x...ekah/81799.jpg
CG125 balance shaft assembly
Anyway, I feel that the vibration is not a problem with the DF engine since it starts occurring at 7500 RPM which is where the power drops off on these push rod engines. I didn't experience this vibration until I started testing with my mini tach. I need to go to a 35 tooth rear sprocket to reduce the RPM at 75MPH indicated.