New 32-36 Running funny

Hello, all! I searched and searched, but couldn't find this exact problem. I'm new to the forum. If this has been discussed, just point me in the right direction. Here goes...
I have a 1987 B2200 Ext. Cab Stick that just got a shiny, new Weber 32-36 today. I've set everything up properly and adjusted everything according to the supplied instructions and via what info I could find online. The mix screw is screwed out 4 turns. The idle is running just rich (Sunpro Air/Fuel gauge and a new O2 sensor installed 2 days ago). As soon as I try to rev it up to 2500 RPM, the air/fuel ratio drops to well lean. Are the factory jets too small? Am I missing a vacuum leak somewhere? I plumbed the timing advance loop into the carb at the designated port. The charcoal can is hooked up too. I'm trying to get this thing sorted for it's last emissions test. It's a tailpipe sniff, not a visual inspection, so the carb should be fine, so long as it's adjusted correctly. Any help would be appreciated.

how did it run before you did the swap?

I think you have a vacuum leak. 4 full turns is too much for the idle mixture screw, instructions on mine stated 2 full turns maximum.

Did you sand the adapters flat using sheet of glass and wet/dry before installing? Did you apply sealant (such as Permatex Aviation, not RTV) to the gaskets, and torque them correctly?

These are prone to vacuum leaks. And did you plug ALL the vacuum ports that are unused?

Chaser, it ran well rich before the swap. Too rich for emissions, in fact. I couldn't find the bad sensor/wire. I did the swap to get some control over how it runs.

Cusser, I'm going through and double checking right now. I'm eliminated everything except the vacuum advance on the distributor.

After a thorough double-check, all of the vacuum lines are sealed. I used RTV on the gaskets (didn't know any better) and I did not sand all the plates flat. I'm gonna try the carb cleaner trick around the plates tomorrow. If it shows a leak there, I'll redo with better sealant and a proper plate sanding. Damned ignorance!

I didn't know the trick about checking/sanding the adapters flat either, haven't done that on mine as I haven't had it off since I learned that from someone else. Plus, last time I had the Weber off and had a vacuum leak, I didn't have new gaskets so I bought rubberized sheet gasket at O'Reillys and cut my own gaskets, so maybe that helped. I also used Permatex Aviation (Ace or O'Reillys) on my rubberized gaskets.

As to the RTV, I had tried that on my old gaskets before I made the rubberized sheet gaskets. Like you're finding, RTV is great for oil and for coolant, but even Ultra Gray RTV is not inert to gasoline. So it made a mess, and I had to clean all that off. So I learned that the hard way.

After a couple nights of trials and tests, I've made some sense of the Weber. Going off Cusser's suggestion that the adapter plates might be leaking, I did the Carb and Choke cleaner test on them. No bogging. No bogging means no leaks. So, I sprayed the entire intake manifold, to see if there were unplugged vacuum ports. No bogging still. And the truck is still running stupid lean. I then called the Redline tech help line. The nice gentleman explained to me that, in order to compete with the cheap, Chinese knock-offs, Weber sets up these carbs for an economical running situation for the smallest engine in the line and that I would need a jet kit. 2.5 hours later, I have a jet kit in hand and start swapping them out. Factory jets for the Weber Redline kit #K675GE are as follows:

Primary
Secondary
Primary Main
Secondary Main Jet: 140
Primary Air

I ended up changing two of the jets, as follows:

Primary
Primary Main

She purrs like a kitten now! The narrow band O2 is saying it's stays just barely rich, at idle or on the go. The issue I'm having now is that I did not pass my initial emissions test, which was the entire reason for installing the Weber in the first place. I failed on the cruise section for CO2. I am allowed 3% maximum. I had 3.81%. In theory, could I not just switch out the main jet for the 150, test it again, and pass? I was also thinking of simply unplugging one of the exhaust air inlet tubes and testing again. I am in the Seattle area and all we have to do is pass the tailpipe sniff on vehicles this old. Thoughts?

Where is your idle mixture screw now? 2-2.5 turns out MAX. How are your ignitions parts? New plugs might burnt off the .81% +. More info please.

Mix screw is about 1.5 turns out. Has new plugs, wires, cap, and rotor.

check your choke spring I had to fiddle with mine to get it to close all the way when warm.