Engine miss at cruise

[Sonny]

I have a slight engine miss. At cruise over 45 it sounds like surging. You can see the miss when using a timing light on the harmonic balancer. I have new plugs, wires, Pertronix ignitor, and coil. My plugs are a little black so not lean. Any ideas to check?

 

[Sonny]

I have a slight engine miss. At cruise over 45 it sounds like surging. You can see the miss when using a timing light on the harmonic balancer. I have new plugs, wires, Pertronix ignitor, and coil. My plugs are a little black so not lean. Any ideas to check?

1978 360
Stock dizzy with Pertronix
RPM air gap
Holley 570 (70/78 jets)
19” vac with 8.5 PV
Yellow spring in vac secondary
Stock block, mild cam
1970 Belvedere

 

[Zeppelin264]

I'd guess your getting arching from your wires to some kind of ground. Look under the hood at night and spray water mist over the engine bay and see if you see a light show anywhere.

I had fairly new Firecore wires that did this. Could see the arch happening all the way up the wire, it was crazy!

 

[Kern Dog]

You can be lean at cruise and still have black plugs. The idle mixture screws, if fully closed, will often result in this condition. Too bad you do not have an air-fuel gauge. They really take the guesswork out of tuning.