ok. so I replaced the cap, rotor and the hei ignition coil. seems to have corrected the issue.

Hi Marcus,

I had my dist cap pop up and the rotor made a revolution and left a mark above the contacts. 

What I noticed from the driver's seat was a back fire and jerking motion and the engine stopped. 
I pulled over and found one of the distro clamps loose. I could lift up on that side of the cap.
I secured it and drove home.  I replaced the cap and rotor and made sure that the clip was seated
properly. 15,000 miles later I have had no trouble like that again.

I must not have had the clip lined up on the groove where it seats. 


All the best from Tucson.

Keith

Take a look at the back side of the old rotor you took off, Marcus....see if you see anything that looks like dark colored lightning bolts running from the center of the rotor out to the screws that hold it on....I bet ya do....

The cap was just loose and the 4 screw clamps would not keep it tight anymore. inside the cap... the contacts were pretty marred up and yes their were black marks on it but more towards the bottom of the cap where. the rotor contact point was pretty messed up as well. the Hei unit that sits on top well the previous owner had sodered the hot wire back on to the metal area that pushes into the dist for contact to the wiring. That was also not making good conection.

One of the major issues with the HEI system is the rotor, or, more precisely, the composition of the rotor. What kind of plastic/composite is used makes a huge difference. While the OE rotors will still have the same failure issue, the aftermarket replacement rotors are absolutely junk in comparison, with the exceptions of a couple of the High Performance ignition manufacturer's parts.
What happens is the electricity from the ignition system naturally wants to find the easiest way to ground....usually that ground is the side electrode of the sparkle plug. Once the plug electrodes wear, the gap widens, or there is an issue with the plug wires, the ignition voltage wants to find a quicker, easier path to ground. The closest ground there is is the two screws that hold the rotor to the distributor shaft.....and THAT'S where the little lightning bolts on the bottom of the rotor come from, and the blackened look of the center of the rotor. The ignition voltage is literally jumping thru the plastic of the rotor, going to ground. I've seen rotors that were so cheap they would melt a hole right thru the center in about a week of driving.

Anyway, the whole point of this is to use the best quality ignition components you can on an HEI system....it could mean the difference between getting home, or getting a tow twuck...
Also, if you happen to have a violent backfire thru the intake, that can blow vacuum lines off, as well as damage some of the gaskets in the intake tract...and if ya have a Holley sitting on top, you can bet yer booty it just blew the power valve all to smithereens....