So, I got the boxer to run on my first try, but it clearly wasn’t running properly and would hardly take any throttle. I was thinking maybe the ignition timing is off, better check that. A strobo-lamp attached to the spark plug wire soon told it’s clear tale: igninition timing seemed to be in spec, but more alarmingly the right side spark plug wasn’t firing at all. I knew the suspect, I had been warned before: the ignition coils of the 1990 GS’s were prone to crack, and will cause problems when wet, or start to fail in other ways. They should be replaced with later improved coil models from BMW. As they OEM’s aren’t exactly cheap, I decided to order a used later design model off eBay Deutschland, and try with that. At the same time, I’ll replace the spark wires, plug caps, too. I have all the parts now, but have lacked time and energy to finish up with the installation and re-run. Busy work and now a flu have kept me outside the garage.