I have had tachometer reading problems for a few weeks. Im pretty sure its my trailing ignitor from online research, problem is i'm not really sure what that even is.

My 82 na rx7 has an msd direct ignition. When i got it a year ago the trailing plugs were plugged into the lead ports on the distributor. A few weeks back i moved them to the trailing ports. Idle seemed to smooth and it ran fine. About a week later my tachometer started acting funny, it would show much higher rpm than engine actually was spinning and then after about 4k the needle would jump around and quickly settle on what seemed to be the right rpm. Today i changed the spark cables back over to the lead ports and it idled smooth and the tachometer went back to working correctly.

So obviously the problem lies in the distributor and not the coils. Does my diagnosis of trailing ignitor sound right? Are the ignitors the two back wings that sit in the distributor and touch the rotor? Is it ok to run the engine off the lead 1 & 2 ports?