If we multiply 6.5 by 12, we get 78 km per hour, which is quite close to 80, these are mechanical meters and some error is possible. This is for GS-150, your CG125 has different gear ratios, therefore it will run at 80 km per hour at a different RPM. Still, 80 km per hour at 8,000 RPM is low for CG125, you should have it checked out.