I million thanks to Manfred (who set up this great site) and to Steve Grisanti who gave the great tip in the discussion board of 2001 under the subject "runs on one cylinder" https://www.tr1.de/tr1_forum/messages_2001/441.html
I bought a 1983 TR1. the 4:th of october but it didn't run on the forward (#2) cylinder. After countless hours of trying to find the cause I was near a nervous breakdown - and then; I found Steve's tip!! It took me ½ minute to mend the bike and it runs just great!!!