How is the rest of the engine?
If there is low compression, ignition problems, or a vacuum leak the best carb will only work as well as the rest of the engine will allow. Compression problems are more apparent at idle.
How is the fuel supply? If the tank is rusty or dirty, the same will be in the carb. If any contamination came down the fuel line or got in the line while it was disconnected, it can hold the needle valve open and cause flooding. Evidence of flooding is dripping gas whenever the fuel valve is open ( a few drops after a failed start or an off idle shut down is normal), black smoke, hard warm starts, poor fuel economy, sooted plugs.
If you think it may be flooding, try closing the fuel valve while it's idling. If the engine idles better before it quits, then it may be flooding or the float set too high.
Something to try, close the fuel valve, remove the drain plug from the carb. Be ready to catch the flow in a clean glass, see what you catch. If it's dirty the tank will need to be cleaned or it will be an ongoing problem.
Next, open the fuel valve, let some gas flow through the carb. Sometimes that will flush any contamination out of the needle valve and stop the flooding. LIGHTLY tap on the carb body with a screwdriver handle while it's flushing.
If the carb appears to not be flooding after the flush, or if you believe it wasn't flooding, and any other problems were corrected to the best practical ability, then it's time to adjust the carb. The engine needs to be up to operating temperature. If it has been run any length of time with the carb flooding it may need an oil change as that will effect the mixture adjustment.
Adjust the idle speed screw first. Idle the engine down to as slow as practical without dying. Usually around 400 RPM. If it's idling any faster the idle mixture can not be adjusted.
Usually on the old updrafts, turning the idle mixture screw (the upper screw) in will richen the mix, out will lean it. The screw is adjusting air bleed, not fuel flow.
I'm not positive on yours, but try adjusting the screw out until the idle quality falters, then back in to best idle. If that seems to be backward, turn it in to falter, then back out to best idle.
You can play with that as needed, the idle adjust is not that critical, and the adjustment is minimal, just try to get a smooth idle at a low RPM. If the engine is not in good health a low idle may not be possible, just get it best you can.
The main jet adjust is next. Turning the main adjust screw (the lower screw) in leans the mix, out richens it. Start at about 2 turns off the seat (gently turn the screw in until it just touches the seat). With the engine at low idle, suddenly open the throttle, listen for the response. If the engine powers up smoothly without hesitation, turn the screw in 1/4 turn, run the test again. Keep repeating, turning the screw in 1/4 turn at a time until the engine falters. Then start turning the screw out 1/8 turn at a time, repeating the test until the engine will accelerate smoothly without hesitation. A single puff of black smoke is good.
Give this a try, hope it helps. Again, get the engine as good as you can before trying to adjust or blame the carb. Everything has to work together.
