One more item to check is the high speed needle on the carb. I'm not sure if it's a Walbro or Zama, but try turning the high speed needle in. Some carbs have plastic limiter caps which limit how rich or lean the engine will run (another government fuster cluck,,,lol), and some of the newer Walbro's have needles with no slot in them at all to prevent the homeowner from making any adjustment at all (for which I've machined a special tool to grip the needle and allow for adjustment).
Regards
Jeff