Car is an 84. Running a 13b with the dizzy on a Weber 48IDA. MSD 6A on the leading coils. The tach is running off the trailing coil, which is connected per factory.

I have breakup while driving, mostly at low rpms. Shows up on the tach as the needle bouncing around while rising, causes rough running.

Does not breakup at idle, rarely will reving in neutral. Mostly an "under load issue"

Can't seem to find any missing grounds.

Any ideas on where to start? I have a spare dizzy ill toss in tomorrow perhaps.

 

How did you connect the wires to the magnetic pickup from the MSD? it should go green to red and violet to green.

 

Is this a FB dizzy or an SA dizzy? Makes a difference in how the wires will hook up to the MSD.

Using stock ignitors?

If you disconnect the trailing and get the tach signal from the MSD is there still an issue?

The tach is not causing the rough running, its just a symptom. So ignore the tach and lets figure
out whats running rough, leading or trailing.

 

84 dizzy. MSD is hooked up correctly. Checked four times.

Stock ignitor for trailing.

Referencing tach, because it may be indicating a failure with the trailing ignition.

Going to troubleshoot some today and report back

 

Are you sure your timing is set properly?

Sounds like it breaking up under load, any chance its preignition?

 

dizzy failed mechanically. Was making very loud knocking noises. Replaced with a spare, runs good. The old one probably had 400,000 miles on it.