1982 G54B carburetor tuning

Hi everyone, I've been slowly restoring a 1982 Custom with a G54B engine with its original Mikuni carb. It runs and drives great, only issue I havent been able to figure out is that it refuses to idle. It misfires horribly, produces a puffs of fuel rich whiteish smoke, and I have to put just a slight bit of throttle input to make sure it stays running. I've been trying to figure out how to adjust the carburetor but I can't for the life of me find the mixture screw. I've looked through the manuals on the forum and I see it labeled, but when I look on mine, it's just a flat piece of the carburetor. There appears to be a plug or something in its place but I'm not quite sure. I've adjusted the idle speed screw and it helps a little, but the mixture is still all out of whack.
Thank you for any help!:))

FYI
I was able to use my corded dremel tool with an end cutting tungsten carbide burr (shaft size like a 1/8th inch drill size) to remove that air/fuel mixture screw plug ( go little by little) and I did it with the carb mounted in the truck... However, that air/fuel screw uses a tiny flat head screw driver ( a smaller jewelers size driver) so I was never able to adjust it yet ~ I been chasing vacuum leaks instead... I have a nice vacuum gauge which I think helps achieve a proper screw setting (adjust for highest vacuum reading..?)

The Mikuni on my truck got a DIY rebuild and I noticed that every rubber piece O rings diaphrams etc were all dry rot cracked etc... The truck had a no start condition and the cause was discovered to be a leaking carb float (there was gas inside the float) which caused a flooded condtion..! I have never gotten the truck to run perfect yet, close but often there is a nagging weird big small med intermittent nagging miss... I am chasing vacuum leaks...

Things that really helped the truck run better were:
rebuilt carb
replaced cylinder head
removed plugged catalytic converter (inside the exhaust manifold of my gen 1 truck)
replaced two coolant sensors
replaced O2 sensor
capped off a vacuum leak

Good Luck, I have a fsm for adjusting a 1984/5 Mikuni but I don't understand the damn pics 'n words & it only covers a few things ~ by trial 'n error I finally found the idle adjustment screw after owning this truck since 2018..! I used a cheap made in china summit racing laser tachometer to set idle RPM 750 + minus blah blah (which when properly set seemed to be or was higher than when I had it set by guess work..!) The engine idles smoother now...

Having an extra original Mikuni carb on hand is helpful when rebuilding one of these suckers ~ please check out my photo albums here at MR50 I took plenty photos of the carb rebuild...

I wish you the best...

The mixture screw is plugged because it's not intended nor required to be adjusted post-factory, and there's no reason that calibration would "drift" over time/mileage.

Adjusting the mixture would just be trying to compensate for the actual reason it's running rich, so better to chase that down, or rebuild the carb, or if necessary, replace the carb with a rebuilt unit (if your area requires a stock carb for emissions inspection) or a Weber swap (better for simplicity, performance, fuel efficiency, and actual tailpipe emissions).