Bouncy lagging tach

[AcampoDave]

Pretty much like the title says. It bounces up incrementally as I wind up the motor. It also reads low most of the time. I've swapped the tach (Autometer) with another identical version. I've swapped the coil, I've tried a different ground. Tomorrow I'm going to swap the trigger wire to the HEI and I'm wondering what guage wire I should use for that as well as the 12V hot. I think it's all wired with 18 guage now. I can't think of anything left to try besides that, but if anyone has a suggestion please let me know. Thanks.... oh and I'm sure the tach itself is set for 8 cylinders too.