Thanks TwinOaks, Jimbob, Tnawrot2 and Trox !!
In the first place I turned down the pressure and, doesn't sew as well as with more pressure, but I can control the work and it leaves less marks. Then I tried to rubbing out the marks with some water drops and the edge of my burnishing tool and the marks dissapear but, of course, appears a shining line... that looks better! :D
For now I will work this way but searching for a best wheel or foot for my adler: (that is no triple, but double feed and it has only one bar for the feed... I think one old owner change parts and things and now isn't all original ) >
I'll continue investigating! but sewing leather meanwhile Thanks a lot guys!