One last thing, have you adjusted your needles lately too?

The first box I made I used thin balsa and made it about 1" or so square. I only made one hole in it just large enough to fit the diaphragm line into tightly, nothing else. Balsa breaths pretty well.
If you are on the rich side you also "might" be experiencing some fuel puddling in the reed area, when you role etc. it all get dumped at once.