The early tachs (70-77) use a D'Arsonval meter and a small tach circuit. These meters are slower and less responsive than the bi-coil meters used in 78-81 Camaro. Even though the early tachs are slower, there isn't an extreme amount of response time as you described. The problem with your tach could be in the meter itself, or a combination of the meter and tach circuit. There is no way to know for sure what the problem is without testing the tach myself. If you would like to send it in for testing I can give you an accurate quote for repair. Just let me know how you would like to proceed and I will be more than happy to send you the shipping address.
Thanks!
Daniel
Thanks!
Daniel