PROBLEM SOLVED. First of all thank you all for your help again... The machine is perfectly thread and nothing is cocked... And now is alive again. In the attached photograph you can see the screw that was causing me a headache... That little -CENSORED- was really little bit loosened (I don't know the reason) and stood out from the shuttle (less than a milimeter), causing it to get stuck.
By the way: the Uwe's video about timing a Cowboy CB4500 and the PDF's of the Juki 441 aren't exactly valid for a CB3200 cause certain parts aren't the same, although I suppose they are good to guide in the process If you know the differences...