Quick question - How does it run at part throttle? The same overly rich sound as at idle? (Does it sound like consistent cylinders misfiring at any engine speed, or just rough & blubbering)?
What is your idle speed? You mentioned there are NO transfer slots exposed. None? So there are only a couple other paths for fuel to get to your engine - The small round idle circuit holes below the blades, (which the mixture screws should control), or the boosters, (which you said are not dripping), or an internal leak/bad power valve, etc. Man, that sounds like your throttle blades must be pretty-much completely closed. I don't know how it is even running at idle. Give it some more air. Try opening up your throttle blades with the idle speed screw, at least enough to where you can see the blades opening a bit, (or better yet, pop the carb off, look at the underside), and set the idle speed screws to where the amount of transfer slot exposed, on the front and rear barrels, is shaped like a square - expose just enough length of slot to equal the width of the slots.

Oh, and I realize you said your shop is warm. Was it heated overnight? Or is the engine possibly still colder? Even with warm air, the intake and heads are cold alky will pool and not atomize or vaporize well. For me, it gets more difficult to light off below 50*, and at 40* or below I won't even bother.

This message has been edited. Last edited by: FootbrakeJim,

Just wanted to close the loop on this. It was not the ignition box. The vacuum well behind the power valve was full of fuel on the primary side and was dumping that fuel into the intake via the power valve blowout preventer check-valve. I temporarily plugged the port in the main body to keep it from bleeding fuel and the engine runs as it should. Haven't had time since getting it running but will dig into the metering block. New gaskets everywhere and the metering block gaskets are the correct 2 circuit reusable holley blue gaskets.

Thanks for the input everyone, this one is new to me, frustrating and humbling all at the same time.

Glad you found it and got it resolved.

Thanks for the update!

LIKE! The follow up/closer to the thread.

2BKING

Yes, glad you found the problem, and thanks for letting us know and closing it out. That is what makes a lot of these threads more useful down the road. If somebody might have the same issue come up years later, being able to see what the actual cause or corrective action was will give them something to look for on their ride.

That's not the first power valve that looked / seemed okay, but wasn't.