Carbon tracking through rotor. More HEI woes.

iScamp said
Need some help with a failed ignition system. I did a Forum search and found one result that might be helpful, I'll get to that in a bit.

Here's the setup:
'72 340 Mopar. Has been converted to use a GM HEI module. Blaster II coil recently replaced as part of troubleshooting. Symptoms occurred with either old or new coil.
New Taylor plug wires, 8.5mm. New spark plugs, NGK, gapped .040". (sorry can't find the part number right now, if it's important to troubleshooting I'll go out and look)

The ignition system has failed twice now. Both times a bad distributor rotor. The car runs great and after 200 miles or so, starts 'missing' and running rough. Changed the rotor and it runs great again. Decided the HEI was burning through the stock chinese rotor. Bought a tan Accel cap and rotor designed for HEI ignition systems. Again,after ~200 miles cumulative driving the engine started running rough (this weekend). Put an old, known good rotor in it (temporarily) and it runs great.

Looks like the high tension voltage is going from the rotor tab directly to distributor shaft.

Someone from a post back in 2014 here on FABO said, 'if it has resistor wires and resistor plugs, they won't do well together' or something similar. I've got both on this car.

Why would the spark go through the rotor? No moisture ever noticed in the cap. it is a vented cap.

I had an issue with my MSD Pro-billet doing the same thing. It actually melted the tip off the MSD rotor, blackened the rotor between the center contact and the tip and really burned up all the plug terminals inside the cap.

Through research and advice here, I found that my phasing was very far off, and suspect that your phasing is off too. When it is, the spark has to jump a longer distance from the rotor tip to the respective ignition wire terminal inside the distributor. That creates a lot more heat than it normally generates.

Take an older cap, drill a 3/4" or so hole between the center terminal and the #1 plug tower and flash your timing light in there. You'll need to either use an adjustable rotor or adjust your reluctor or trigger wheel to alter the phasing.

Once I did that, the rotor and cap terminals began to look normal again.