Timing mark moved? Shows if you use cyl #2?
 

Totally stock '81, ecm works, no codes, E4ME carb. Complete tune up. Runs pretty well, but I read that the timing can be advanced from std 6 to 10 - 12 BTDC.

So I go for a ride, get it up to temp. Shut it off, hook up my light to cyl #1, unplug the 4 wire plug. Fire it up, and no mark can be seen, even though I marked it nicely on the balancer so I could see it. Cleaned off the gauge so I could read the degrees as well. WTF? Engine idling nice, runs very smooth all the way up. So I put the induction wire on #2 wire, and there is my mark! :crazy2:
So I keep the light on, and turn the dist....I can turn it clockwise and the engine begines to stumble, turn it counterclockwise and the idle goes up, to a point and then starts to stumble again; if I leave it at the highest idle rpm point, my light says 11 BTDC.
Has my balancer rubber gone and this is why I am seeing this? I plug the 4 wire back in, and it starts and runs just fine....have not road tested it yet, it started to rain, and car is too clean for that. Perhaps tomorrow...

Any opinions?

Do you mean that you connected to the plug beside #1? If so that is #3. Are the wires going from the plugs to the correct place on the distributor? It is possible that when you connect to #3 that it is getting its spark from #1 on the distributor.

Check your wiring to be sure.

I'll vote for balancer rubber.
What you describe happend to me while drag racing in the 80s so I timed it by ear for that meet.
Then the outer ring fell off...lucky i had a balancer shield or it may have lodged in someones head.

Bad balancer (elastomer disintegrated) or the wires on the distributor have been re-clocked.