I cleaned the carb very well, and it wasn't even dirty. Cleaned fuel tank. Fuel flows well. I'll check the in line filter. Plug is new.Worn or wrong spark plug?
Also, the fuel tank likely needs to be removed and cleaned. Check the fuel line because they installed a slip in line fuel filter/ strainer on many models and they would get clogged up. Good engine but had some design flaws that created problems like you describe.
Aside from that, you say the carburetor is "good". Does that mean you removed it and properly cleaned it?