RE: Walbro or Tillotson Carb
Sometimes the best carb for your engine is not the one supplied by the manufacturer, sometimes there is nothing wrong with the carb or make, but simply the venturi size does not suit the engines design.
I have swapped "bad carbs" onto another brand engine and ended up with a great running engine and more rpm than what was supplied by the manufacturer.
I find its worth experimenting with diferent carb/engine set ups as the carb can make a huge difference to power output and how a motor runs.