well, i had that kind of problem. many kits come with not such quality mics, so that might be the problem, but could be something else, if u have a big signal, then you hear it(considdering that when you blow into the mic you create a bog singnal), but a smaller signal from the mic like the voice is not transmitted. try r1(47k) ttry to replace it with a smaller one, a 33k or 27k, it might work. an check the bc547 transistors, some of them have a much smaller gain then on the catalog.
but still i would try another mic, buy a cheap one, but is you see the same results it means its not the mic.
also check c1 and c2, and maybe put a 47n in place of c1