@ferox: Thanks for the detailed reply.
Let me state the responses in sequence.
1. Now I'm really confused between the terms "Idle Mixture Screw" & "Air-Fuel Mixture Screw". Just for the clarification, I have been referring to the screw at the back of the carb, I think angled at 45 degrees
With a bit of throttle, the engine smooths out but still has black smoke.
2. I did try my best to clear all passages but didn't have any air compressor so skipped that. Maybe the carb needs another round of cleaning. It's just that the gaskets are a tedious work. I had made them out of thick paper sheet
3. It's not very clear, where exactly is fuel coming in to the barrel. I'll need to take a closer look again and will let you know on this.
4. About the power valve, well it didn't have any such valve or solenoid valve. That was my prime query whether it's missing the valve of this particular model didn't come with any valves.
hashim5003 has confirmed that this model doesn't have any power valve, and I'm not missing any jets as well.
5. About the nipple at the back of the carb, yes there's only one vacuum line. I thought the other might have been broken, but it doesn't have any vacuum to it. I did plug it with a screw anyway
6. There's just 1 electrical connection on the carb, and that is the anti-dieseling switch. Other than that, no solenoids, valves or plungers. I'm worried now. santaclaw has the exact same carb model but opening up a working carb is definitely but risky.