The float level is critical, as it affects how much venturi vacuum is necessary to make the transition from the idle circuit to the midrange and high-speed systems. The gasoline will find its own level in the carb body, filling the passages with liquid gasoline, which is then atomized as it enters the airstream through the venturi. A too-low float level results in a flat spot just off-idle, as the idle system can no longer support the engine's fuel needs, and the high speed system hasn't gotten into full operation yet. Try tweaking thd float up a little at a time, and stop just before the fuel level gets high enough to trickle gasoline out of the venturi at idle speed. Also, try to determine if the carb part number is correct for your engine. Similar-looking carbs often have very different internal calibration, and all the tinkering in the world won't help a carb that's being used for the wrong application!
Jerry
