Any smog stuff hooked up to the engine?
Have you tried switching vacuum ports on the carb(for vac advance)?
Do you have an adjustable vac. advance canister?
What kind of thermostat(heat range) you got?
How about plug heat range?
6sal6

Yeah, I'm pretty sure it's either a timing issue or a temp issue.  I don't know what thermostat I have ("stock"?) but it opens, I get water flow, temp gauge is sitting in the middle.

Spark Plug is Autolite 45.  It looks normal. No deposits, slight toasty brown ceramic, gray/white electrode.

I'm running the ported vacuum, not the constant one.  I did run constant earlier but the pinging was worse.
The carb is a reman Autolite/ Cardone 30-2895 single vacuum, but I don't know if it's adjustable because I don't have any long allen wrenches.  What size? I read 3/32" somewhere, but don't know if it was for Autolite distribs. The distr is twisted such that I wouldn't be able to get a long wrench in (interference with AC compr) and I don't want to take it out until I know whether or not it has adjustable vacuum.  Can someone help with this info?

I did a warm-up drive, got the pinging problem, disconnected and plugged the (ported) vacuum hose.  The acceleration from rest was not as crisp, but seemed okay once I got rolling, and the pinging was gone.  Obviousy, I'm getting too much advance at warmed-up temps.  Is there a problem running without vacuum advance? Will it hurt (or even help) MPGs?  Why doesn't it ping while sitting still?

Thanks...

Last edited by Physics Doc (10/06/2013 3:20 PM)

What's up Doc?  (Sorry, the devil made me do it!)
The symptoms you describe are the symptoms one would encounter with a partially plugged exhaust system.  Are you running duals, or is there a "y" that joins the two banks to one pipe.  When you are at cruise speed, and you try to accellerate hard, does the car respond as it should?  Or is it the accelleration sluggish and pinging?  Typical partially obstructed exhaust.
Good Luck

"And now a word from your cam/ignition doctor!"
Doc........take a couple of asprin..never mind.
I think its in the vacuum advance. (Cause it went away with it dis-connected!) Here's what I'd do.....
Pull the distrib and "re-stab" it so the vacuum advance can is more accessable,more toward the front of the engine. You may have to re-clock your wires so no.1 is aligned with the pointy end of the distrib button.  You're gonna need a long enough allen wrench to go up inside the hole where the vacuum hose fits.  IF its adjustable you will save a few bucks,if knott....its a good time to order one from Summit/Steves Mustang......Pretty cheap really.
I'd start off with the adjustment about mid way and do a test drive and screw it in a couple of turns and see what happens........if no good screw it out a few turns....until you get it to not ping with the vacuum hooked up. "theysay" once you get the vav.advance really tuned in.....car will run better and you should pick up a few MPG.
The reason it won't ping in the driveway????......There is no load on the engine. Simple when you think about it.
Another option would be take it to a shop that can set up distribs on a distributor machine.
Let us know what happens!
6sal6

Your description of your plug's color sounds perfect, so I doubt you have any carbon buildup in the combustion chamber. The other classic diagnosis is too much total advance. Since you are using what passes for premium these days, it sounds like you have way too much advance. How old is your balancer? The outer ring with the timing marks may have slipped. It's a lot of work, but finding true TDC with a screw-in stop will answer the question. Disconnect the battery and hand turn the engine please.

I'm making progress.  Thanks for everybody throwing in their expertise, too.  Lots of good tech stuff here.

I checked at O'Reilly's and they had the same Model dist. in stock, so we pulled out some allen keys and found that a 1/8" would engage the advance adjustment.  I went home and tried a 1/8"...it wouldn't even go in the hole! Tried a 7/32" and nothing....hmmm...let me try 3 mm. Because it was on a big flip-out set of keys, it wouldn't fit, so  I got over my "leave it put together" anxiety and pulled the distributor (after making many marks) and restabbed it in a better position for the vacuum hole.  The 3 mm fit and engaged something.  Oh, wait...what are my current settings.  Using a vacuum pump I tested that the advance arm immediately started moving with any vacuum at all (< 1"Hg) and was fully in at 13".  A turn CCW and it's coming in a little later.  I made several turns and got it to 5"Hg before it started advancing, and it took about 20" before full advance.  Time for a test drive.

Overall, it solved the pinging problem.  AFter a good warmup period I cruised several miles under different load conditions with no ping except for extreme acceleration at high speed.  A cruising accel from 60 to 70 was nice and smooth.  The one problem is a brief sag when starting from rest until the engine hits about 1200 rpm.  I'm idling in gear at 900.  I probably need to turn the vacuum back CW a little bit so it comes in earlier, but that's a detail adjustment now.  My big problem is solved.

Now, if I can just get the base timing down a few degrees.  I did check the timing marks this summer, and AFAICT, the 0 BTDC mark is true.  I did not have an "official" piston stop, but I did use the same technique with fine pencil marks on sticks in #1 and masking tape on the balancer .  I actually did not look at the numbers on the balancer until I was through making marks.  I was pleasantly surprised that 0 was dead center between the tape marks.

You might also be finding a hole in your mixture off idle related to the adjustment of the accelerator pump or even the sqirter size.  You may also be slightly lean on the mixture.  Try opening the two idle mixtures about 1/8 turn and try it again.  Without a dyno looking at A/F ratio it is hard to know whether you are fighting timing versus mixture.  A hesitation like that is also seen when you connect your advance to manifold vacuum versus the timed port on the carb.  When you hit the gas when connected to manifold vac, you loose the advance and it falls on its face - which I learned from inexperience.