Two questions:
1. if you did bedika without bitul and it turned out that you missed some chametz will you be oiver baal yiroeh or not?
2. erev pesach before chatzos you walk in the street and you see a piece of bread that's hefker can you make a bracha on biur chametz and be mikayim a mitzvah?
Mendy Kaplowitz
Shalom and thanks for your questions.
1. If the Chometz was hidden, there is no Bal Yera'eh, but there is Bal Yi'motzei. See Gemora 5b, and Rashi 21a D"H V'ee Tana.
2. If the Chometz is Hefker and not in your possession, you have no Mitzvah to do Bi'ur. The only way you can have an obligation to do Bi'ur (and recite the brochah) is if you somehow acquire ownership. This of course is forbidden, since for those moments until you destroy it, the Chometz is in your possession.
Kol tuv.
Y. Landy