OS 61 sf max carb problem
The main thing about your carb is the position of the slotted screw with the eccentric head. That's the one at the top of the picture. When the slot in the screw is straight up and down, your idle mixture is in the center of its range. Turning it clockwise will lean the idle mixture, and turning is counter-clockwise will richen the idle mixture.
If the carb's been disassembled, the mixture control assembly may have been installed at 180 degrees to the correct position. This will cause all kinds of headaches in running.
If your engine will throttle nicely from idle to top RPM, and has a good idle, then the assembly's installed correctly.
A smoke trail may or may not develop when the engine's running well. It depends upon the fuel used, the exhaust system, and the weather. You can have an engine running very well with little visible smoke. Depending upon the fuel, you can have a lot of visible smoke and still be running too lean.
Listen to the engine carefully, do the 'pinch' test while setting the engine. If you give the fuel line a quick pinch at full throttle and the RPM jumps a bit, you're rich of peak RPM. If it sags or stays the same, you need to richen the high-speed needle until you get a slight jump. Listen to the engine carefully when it's in the air, and adjust the mixture as necessary to allow for the RPM increase as the engine unloads.
We usually ran the O.S. Max .61 SF engines on our test stand with a 12x8 APC prop, 10% Omega Fuel, stock muffler, and an O.S. #8 plug. We'd see RPM in the mid- to high-11,000's. Any idle below about 2,700-2,800 was considered 'good'.