Installed new coil, now the tach acts funny

I have used a tach buffer cct that I got from Peter Serio, a fellow in the US that repairs car instruments & gauges & knows his electronics. I have used it with HEI dists that are used with cars that originally had points. It is a bit more than a resistor....but easy to consruct for a few bucks. It has 4 res, a diode, transistor & a cap.