I suggest you consider these two tread - well okay "threads" - which I just happened to have started:
The first has to do with the in tank filter.
http://www.peachparts.com/shopforum/showthread.php?t=124027
The second has to do with the replacement of a leaky primer pump, which allows air to get in with the fuel. I had a similar loss of power as you have described.
http://www.peachparts.com/shopforum/showthread.php?t=109076