I would be concerned about finding excessive crud in the filter screen. Some of that crud could have got through the screen and partly plugged some of the finer fuel passages in the carb. This could be the source (or part of the source) of your inconsistent runs. While you could rebuild the carb, in this case I think I would recommend a new one so that you can completely eliminate the original carb as a source of the problems. Once plugged, it seems that many people have problems getting all the crud out of a carb. Of course, the engine being used might warrant you doing a complete inspection, clean and reassembly from one end to the other. Remove and inspect the cylinder and piston, check bearings, etc. An air leak could also cause your problems so a careful inspection and replacement of all the gaskets would be in order. You might want to split the case and reseal that surface also to eliminate all sealed surfaces as possible leak points. Good luck ..... the problems you are having are not common to this engine.