Need more info about your cam. 

I heard back from the carb builder today. His initial answer, without seeing the carb, is that the carb was calibrated for non-ethanol fuel of 17 years ago.  He thinks modern non-ethanol fuel is different enough to cause the problems I experienced.  Personally I don’t believe his theory but I’m sending it back to him for rebuild/recalibration anyway. After I get it back and get it fine tuned to my engine I will do a chassis dyno comparison between the two carburetors. Should be very interesting to see the drivability differences and actual power difference. I’ll update this thread after I get results. 

Does anyone know any tricks to darken magnesium?  (Other than letting them age 20 years)
Ideally DOW-9 would be my best option but I can’t find anyone in the Pacific Northwest that does it.  I’m looking for a dark charcoal or mat Black look.

I’ll try that but I think the problem is after the transition.  After the throttle plates have already uncovered the slots and the idle ports are not a factor. 
But I’ll try anything. 

Problem still exists.

The original tune was the same tune I started with.
I triple checked every port/slot/orifice and made damn sure everything was sealing and there where no cracks or leaks. I’m 99.99% confident everything is assembled correctly. 

This is the result (same as before)
1. Idle is good at 1000 rpm and 11” vacuum at 13.7 to 1. Four corner idle mixture adjustment  (1 +1/8 full turns out) and all 4 throttle plates are just barely exposing the transfer slots. This is where it has the most vacuum)
2. When I smash the throttle from idle it goes lean 20-1 for a split second. Like the squirters aren’t providing enough fuel to compensate for the blast of air. (Running black and orange cams)
3. WOT is 10.5 to 1.  Still too rich. (Primaries and maybe secondaries too large)
4. Cruising is 12 to 1. Still too rich. (Primaries too large)
5. Roll into the throttle from cruising speed and it goes super lean 17-20 to 1. When this happens it snaps and crackles for 1-2 seconds then goes rich when I hit WOT.
6. I’ve tried 4.0, 5.0, and 6.5 Standard flow power valves. Same result. 

It’s like the power valve isn’t richening it up under load.  PV vacuum port is clear and flows freely.  All PV ports are clear and PVRC is .0600 like the carb manufacturer recommended.

Carb manufacturer recommending sending to them for rebuild but that will be a 2 week turn around.  I would like to avoid that.

I found more info on the carb.
It’s 860 CFM built by Pro Systems. It is built on a Holley HP format with some billet parts.  They sent me all the specs so I can go back to a starting point after I install new gaskets.  Hope to have the gaskets installed and road tested later today. 

Now that makes sense.  I’ll check my base gasket.
I don’t think my transition slots are providing fuel.