Solved: Sudden rough running

I have a good ending to one of those “Help!” Cougar stories. My '68 J-Code 302 abruptly began running rough, barely able to get out of its own way, from idle on up. It’s got a Pertronix conversion and a rebuilt 70s 4300, and my first thoughts went to bad fuel and/or ethanol damage. I even made out a trial order cart for a complete all-stainless tank-to-carb fuel system from WCCC to price it.

I pulled all 8 plugs, hoping to catch one of them sooted (all good-looking, bone colored). I changed the fuel filter. I procured a carburetor refresh kit, figuring the latter would be a good idea regardless of what I found. The distributor cap looked good but I was perlexed by a lack of the usual faint spark burn marks on its terminals, despite the clean spark plugs.

A dim bulb went off in my head. In the 70s, I had one Autolite distributor produce similar intermittent symptoms that arose from a vacuum advance plate’s pivot bushing wearing oblong. Fix that, and blam, that car’s problems disappeared. This advance plate looked solid, so I popped off the distributor cap again and replaced it and the rotor with new ones as an experiment.

Blam, ! Problem fixed, 302 back to its normal happy running. So what had I missed? This time under the cap I grabbed the distributor shaft and moved it side to side. Found the problem; it has at least .080 of side play (bad upper bushing). The old distributor caps’ aluminum terminals were getting clipped by the rotor’s tougher brass just enough to shave them back over time! The gap had simply reached a critical size where even the Pertronix couldn’t arc over it reliably. I squinted and sure enough, there were tiny aluminum shavings down near the advance plate which I had missed at first.

I’m replacing this one with a Cardone “rebuilt” for now and will swap the Pertronix stuff over when it arrives. Moral of the tale?

  • Never stop asking “What the hell’s the matter?”
  • Every episode, even if if you’ve been working on your cars since summer 1969, is new.
  • Never attribute a car problem to something you can’t see before you exhaust the things you CAN see.

This is a great time to point out that the Pertronix ignitor electronic replacement module offers no more spark than the stock points. The Pertonics simply doesn’t wear out. Other than that it offers no advantage over the stock points type ignition.

Sounds like you really have identified the problem thank goodness.

Royce is correct about the spark intensity, but the Pertronix is some what immune to distributor shaft wobble. A distributor shaft with .080 wobble results in the points gap being all over the place. When you use a dwell meter, and see the reading drifting around, you are seeing the changes caused by the wobble. If the wobble is modest, the Pertronix may work great, when the points no longer will.

Here’s a fix for your problems:

https://www.ebay.com/itm/NOS-1968-302-AUTOLITE-DISTRIBUTOR-C8OF-12127-C-DATE-8F13-MUSTANG-COUGAR/392007699804?hash=item5b457acd5c:g:h1IAAOSwAQBauRPA

You said it! I found that and am watching it for a future payday.

(Added later: The 8F13 date is likely too late for my Cougar, built early June, which is remarkable because mine is a rather late San Jose build.

Won’t stop ne from buying it if the whim hits me -

My father used to put bushings in the old Load-O-Matic distributors on early Falcon 6 bangers. I think he used a hand reamer to fit them if I remember the process correctly. He said that the later distributors had an oil wick and reservoir that the early distributors lacked, but no one remembered to add the oil.

Glad to hear it.