My new Edelbrock runs rich!

Ahhhh, the smell of unburned hydrocarbons

Though it sounds like your situation is bit overdone, part of the "manly" aspect of a Pantera is this exotic still uses a carb, not no new and fancy EFI, perfect fuel ratio delivery system.

Personally, I LIKE the lumpy idle and the gasoline fumes that sort of says THIS car is a bit rough, but ready to open up and use ALL that fuel at a moments notice.

On a practical note, all aftermarket carbs are supplied over rich, so they don't have to answer to an owner's claims that "HEY, your lean carb ruined my motor!!"

If you had not dialed that carb in before the altitude upgrade, I suspect you are now WAY rich.

My 2¢

Larry

The Edelbrock hotline guru said to screw down the idle mixture screws until it starves for fuel, then back the screw out a touch!??? Better, but I still wear, Ode de par-fuuumes!!! No dates for me after a long drive!!!

And that hotline guru is likewise not going to risk you leaning out your motor and by trying to address an over rich condition by only tweaking the idle circuit he really didn't get near the problem, which is most likely your main jets.

Corporate lawyers have ruined this country.

You need to get some sort of A/F reading.
Edelbrock makes a little kit for that.
You need to install an oxygen sensor in the exhaust to use it.
It sounds like a silly idea but thed do actually help you figure out what is happening with the carb.

Would switching over to a holly 500 cfm solve this problem or should I jet the carb to 12% lean vs the current 8% lean?? My auto parts store is willing to do this for me??

500cfm wll kill a 351 Cleveland

Beware blindly leaning 8-12 without valid plug chops or O2 sensor data.

One has to figure out which circuit needs the leaning and by how much.

The procedure for a Holley is well documented, there are 8 to 10 elements to tune even for the basic models. Can't advise what to do with the edlebrock but I say beware any advise that oversimplifies it.

The tech's advise to lean the screws likely only affects idle and tip-in, and has little effect anywhere else, and thus looses all credibility.

I think the problem is solved. I adjusted the pair of floats to spec. The carb adjusted just like the thousands I have adjusted in my past. I drove it and my eyes were dry and I diden't smell like old car fumes. The backfiring is almost gone too. I pulled a plug to get a reading and it was a light chocolate brown. So far so good!?!?!?