At the end of an extremely rainy and windy weekend the sun came out and I could spend some time troubleshooting the Wartburg. I removed every electric connection I could find under the bonnet, cleaned, added some copper paste and put everything back. The only difference was that the horn/fanfare started working
Apart from that the car was still coughing. So, I thought this must be a vergaser problem after all. I found the air mixture screw and turned it anti clockwise one full turn and the car was running much better
I turned it a bit more and the car is now running what I think close to perfect
Could it really be this simple? I don't know. Tomorrow I'll drive the car to work, 6 km's and then I should know if my adjustment was as successful as I hope. By the way - how many turns should normally the air mixture screw be turned out on a well working Jikov? Now I am off to post another question in the electrical part of this forum.