On the ground, adjust the high speed needle for maximum RPM then back it off a few clicks (richen it) until it drops 200-500 RPM.

The adjust the low end until you get a smooth, prolonged idle, good transition and smooth running at part throttle. Remeber that the LA's carb has an air bleed low speed mixture screw. This means it is opposite of most other carbs. In other words in is rich and out is lean.

If that still doesn't do it, look at things like fuel lines (including inside the tank), glow plug, trash in the carb, etc.