HEI Distributor with Sun Tach II

I have a Sun Tach II that I first installed in my '66 Mustang with my 200 cid, when I installed the petronix II electronic points and coil. The tach was steady and dead on. Never had a problem.

I replaced the stock distributor with an HEI model and the tach is all over the place. Some days it works fine, others not too accurate. I have had three of the cheap Chinese distributors that had a lot of problems with the tach. I upgraded to a Performance DUI distributor. I am please with the performance of the distributor, but the tach is not always consistent. One day it's fine, others it's not. Not sure why each day I would get different results with the tach. Are these older tachs not compatible with the HEI distributors?

Anyone else had this problem? Connections are all good and so is the ground.

let us know where U wired in your tach

The distributor has a tach feed. Wires are soldered in to the clip, for the tach so I know it is a good connection.

Try another tach.
I have a SunPro 11. It has worked fine on a MSD-6al box & HEI distributors.
You are loosing performance with your DUI. All they have is a generic curve one fits all.
My HEI'S are custom calibrated for your engine combination. Just for info.
Get a new tach.