Bernd, you saw how mine didn't want to start when the air pressure was up too high? Start it at less than 5 PSI, and then crank it up to about 20. Once it's going, you can make it scream, but starting on high doesn't seem to work.
It likes to be loose, and will have problems if anything is too tight. So, spray it with your favorite lube, and run it at high speed for a few minutes, then clean it all off, and it will tick over slowly. Mine would barely run at first. Now, after running for an hour or so, I can get it to go on lung power.