Mayor Bloomberg’s decision to fire Cathie Black, his unpopular choice for schools chancellor, hasn’t done much for his approval rating, a new Quinnipiac poll found.

Bloomberg’s overall approval rating was 40 percent positive and 49 percent negative, not much different than his 39-51 rating two months ago before axing Black and before he launched a multimillion-dollar ad campaign to boost his image.

His handling of the school system got a 64 percent negative rating.

Respondents with kids in public schools gave him a 78-20 percent thumbs down.