Pertronix 2 slight miss?

[Darrman]

I just completed my 4brl conversion on my 390, now I have a Holley 600, Edelbrock performer, Pertronix 2 points eliminator and the Flamethrower coil. Here is the thing, It will start and run great, no problem there, thing is that while its running everyonce in awhile there is a noticable hitch in the exhaust note, the tach jumps from 800 to 2k instantly (this is electrical, the motor does not speed up) and the timing light will miss a flash if you are setting the timing. This seems to be a electrical thing, but what? I am running the timing at 10 degrees, it does not like 8 anymore.
Everything ran great with the points, this Pertronix seems pretty straightforward, so what could I be doing wrong? I gapped the module to 30, triple checked that.

[convincor]

The last Pertronix I installed I had to tighten up the air gap a little or it mis-fire constantly on a couple cylinders.

[Darrman]

Thanks for the info, I did tighten it to 28. However before I could see if it would improve, the coil quit on me. I slapped the stock coil back in and the problems are solved, runs great!
So I had a bum coil the whole time, I am hoping to exchange it.

[Supermike]

Was your coil a Pertronix coil? I installed the "Flamethrower II" coil in mine and have noticed a little hitch, too... never thought to put my old coil in and see if it improved.