Scott you are right about the dough being overfermented. I knew that but didn't piece together that being part of the reason the pizza burned so quickly. I couldn't figure out why the pie burned in 30 seconds when the hearth temp was just 650. It didn't make any sense until you posted that bit.
This dough is the same dough I posted about here. Reply #3http://www.pizzamaking.com/forum/index.php/topic,11210.0.html
The dough was a same day dough made with about 10% starter. 10% starter is equivalent to using about a 0.4% ADY according to my conversion. It was bulk and proofed at room temps (covered with a moist towel) for about 14 hours. Surface dough temp measured 65F throughout the entire proofing period. I meant to only proof it for about 9 hours or so, but let it go to 14 based on the dough temp being consistently 65F. It didn't look overproof meaning that it never deflated as some of my past overproof doughs but when I handled it, it was almost unmanageable. It was very pliable and extensible. "The lack of yeast activity as a dough overferments isn't the result of lack of nutrients, but a result of an alcohol rich (and possibly acid rich) inhospitable environment".
I absolutely agree with you. Here's my explanation of what's going on. I may be repeating some of what you and Peter stated already but this is how it makes sense to me. If I'm wrong or if you agree you can let me know.
At some point in fermentation, the byproducts create an inhospitable environment dramatically slowing down and eventually ceasing yeast activity. As Peter noted, the byproducts including the pretease enzymes soften up the gluten structure making the dough very pliable and extensible. Not only do you get dough softening effects but the enzymes also have a proteolytic effect on the proteins and sugars. They break down the proteins and more complex sugars into simpler sugars. This dramatically increases the availability of the sugars (not being used by the stunted yeast) leading to burning.
To try and answer some of your questions.
-Yes the top vent is closed. I have replace that with the new vent cut out right above the rim of the lid.
That new vent is 1"x6" so it's not big enough to load a pie through.
-I have centered the stone so that the gap is even all around. I plan to put a stone or metal lip right under the lid vent to block that airflow to direct it towards the back and sides of the stone as Tampa suggested and as Pizzacraver has done.
-I do plan on starting with a lower hearth temp. 500F sounds good. Thanks for the suggestion.
-The burner is a 160K BTU burner. It will pump out plenty of heat for neopolitan, but until I can get the top heat to be at least equal or higher than the hearth, neopolitan is out of reach. Once I can equalize or get higher dome temps (which may not be possible) I'll should be able to do neopolitan. If it turns out that I can't, I'm ok with that since I like the lower temp bakes better. I create the nearlypolitans in the home oven as is.
-Great suggestion on lowering the temps between bakes. I may take the lid off and lower the heat dramatically to get the hearth temps back down to 500? I may also swipe the hearth with a wet rag. No worry about the hearth cracking since it's split bricks. Load the pie at a hearth of 500F, then crank the fire up to get the surrounding air super hot. This technique may be the key. Thanks Scott.
-I can't put a 2nd layer of firebrick b/c it would not allow the lid to shut properly or close the gap between the lid an the top stone. What I can do is load the pan below with more ceramic briquets or a smaller firebrick stone. This will create the 2 firebrick layer you are talking about.
BTW, the pan is 10" and the hearth is 12", so there is a 2" difference.
-I'll double check the clearance b/t the hearth and the sloping lid to make sure it's not blocking airflow and report back later.
Thank you for your input.