I’ve also got a 77 R75. I’ve been across the US and Canada on that one.
What surging issue?
Discussion
The 1100 oil head had an issue where if you were holding a steady speed it would speed up and slow down. Had something do do with the fuel injection. It was worse at sea-level. https://www.bmwsporttouring.com/topic/9204-what-exactly-is-surging/
Interesting. There’s a guy out of Germany on FB that reprograms chips for 1100s. If I had one I would try something like that. He gets great reviews.
I followed a lot of it back in the early 2000's (mine was a 99r... When I first bought the bike we lived in El Paso and it ran great (must have been the elevation) when we moved to Virginia is when it got really bad. I tried several of the trucks with the throttle position sensor and what not and still couldn't get it to stop. They say twin plugging also helps. I ended up selling it for a 2002 triumph sprint st.