splitting files from default to named branches

[RAPPAZ Francois]

I'm learning Hg and had played with a few test cases
 
I have defined named branches and then have added files to them,
in mainrepo:
hg branch A
hg branch B
...
hg branch common

Then 
hg update A
hg add "files path for A branch"
hg commit -m "A branch defined"

hg update B
...

And I can clone these branches and common files in distinct A B C repos

hg clone ../Arepo -b A -b common
hg clone ../Brepo -b B


And I can pull / push between main and these repos

In my non-test repo, I have added all files to default. I would like to split theses files between say two named branches, A and common, but that does not seems to work: if I clone the repo all the files are copied.

Is there a way to split the files in default in different branches ?

Thanks 
François