It sounds like you may have run the engine lean a few too many times, and now it's toast, but it could be a number of things, like air leaking around the needle valve or around the front bearing, or it could be a pin hole in a fuel line...

It would be best to have someone experienced look at it. You can not however, expect that once someone with experience tunes the engine, that it will be set right forever. These things have to be re-tuned periodically, especially when you have temperature or large humidity changes.
Dennis-