Thanks for your answer.
It is (was) a Toni Clark Piper PA18 2.8m with zenoah 62cc.
May my way of connection be the cause of the malfunction.
During the second flight I was testing the Flapsettings in combination wih the elevator. More power was then requested. Few seconds later the Malfunction started causing the crash.
Do you advice another Powersytem for this kind of plane?