Hi maxgerhardt.
Thanks for your quick responce. 
Sorry for the wrong Community 
I have tryed your suggestion, except for one thing, I did not wrote an under score between PB_6/7 !!
I wrote:
Serial.setRx1(PB7);
Serial.setTx1(PB6);
Will try it out.
And move to Arduino core
Thanks a lot
/Jens