Help with Ignition / Backfire issue (fixed)

[skidd]

I need some help with an ignition issue. I sort of know what the issue is, but I can't figure out the cause.

The car is road worthy, but not yet road legal. I've only had it around the block a whole bunch of different times, both in GoKart and now BodyOn phases.
Prior to yesterday, it ran really good. Good idle, easy starting, plenty of power, no hesistations.. etc. Everything worked fine.
I have a remanufactured distributor from a 1995 Mustang. The one with Hall Trigger sensor, and vacuum advance.
Wired with a 1981 GM HEI 4-pin ignition module. (yeah... I know)
Sitting in a 1999 Explorer 302 with Weiand Manifold and Summit Racing 600cfm vac-secondary carb, and e303 cam.
Like I said, she's run really good up until now.

Short Version:
With vacuum advance connected to timed port on the carb, major backfires with any throttle input.
Initial timing is set to about 10deg (I think).

Long Version:
Yesterday while fiddling, it started running really rough, and died. Would not start. Nada.. nothing. Could not get it to re-fire. It would seem to try, but not fire.
I diagnosed a spark problem. I was getting a really weak yellow spark (using one of these). from the coil, and nothing at all from the plug leads. Assuming it was the coil, I went to NAPA and got a new Echlin IC24 E-Core coil. Just in case, I grabbed another HEI module too. Swapping out the coil did not fix anything. So, I swapped out the HEI module. That seemed to fix it... in so much as.. now I was getting a good spark on the tester at the coil lead. But really poor spark at the plug leads still. ??? Still wouldn't start. Ran to O'Reilly and grabbed a replacement cap and rotor... opted to upgrade a little for the one with brass terminals over the cheaper looking one that came with the distributor. It was killing me to replace pretty much new parts, with other new parts, but so be it.

Varoom! At last.. it starts!! and seems to idle great. Until I give it just a little throttle... coughin and spittin.

?? WTF is going on!!

I re-checked my timing.. and it sure looks pretty dang close to 10deg BTDC. I say it looks, because I had to make my own timing marker, and It's possible it's off by a degree or two.

Here is where I finally got somewhere.... I pulled the vac advance hose to re-check the timing. Forgot to re-connect it, and when I stabbed the throttle, it didn't cough. I thought I had it licked!! Until I re-connected the vac line.

So.. my current situation. Starts fine, idles fine, backfires under load or just partial throttle.

My Diagnosis:
Failed / Faulting Distributor. But in what way? Is the vacuum advance mechanism capable of failing in such a way as to way way way over advance the timing? Which would sure explain the backfires.

Here is a quick youtube video I shot of it doing that backfire with the advance connected.
http://<a href="http://www.youtube.c...W05VusWwe0</a>
https://www.youtube.com/watch?v=3W05VusWwe0
- Initially with vac advance disconnected. running well.
- Then, vac-advance re-attached. Runns like crap.
- Then again with advance disconnected, and left hanging. It's connected to a timed-vac port on the carb.

Anybody have any ideas?