Hi,
One quick thing you can do if you have another engine is barrow the carb off of it. It doesen't matter if it is much smaller, at least it will tell you if you have a bad carb or not. It will still run ok, just not as fast. Make sure that you dont have leaks and the pulse port is open into the case. The HDA 23 was used in the Sachs saws and is 13.49mm. Any good Walbro about this size will give good power for flight.

Dave