Thanks for trying to help but I`v solved my problem.
I just purchased the motorcicle and some neighbors that have a garage and the passion for engines come`d to congratulate me. I told them about the problem and they where very happy to help.
But if you want to know what happend ; they told me that the garnish(suite) from the so called gas pomp on the carburetor was rotten.
P.S. I hope you undersand my english. Thanks again !