14979 wrote: Smoke only on off throttle sure sounds like valve stem seals. The engine develops a might big vacuum when the throttle is snapped closed and the engine is back driven by the tire. Valve seals are pretty easy to replace on an Airhead.
I don't believe BMW ever used seals on the valve guides of the air cooled engines. But I agree with you that it could be worn guides in need of replacement, but without knowing the mileage, it's difficult to say with any accuracy. FWIW, my R100GS had about 60k miles on the previous valve job when Ted Porter replaced valves and guides, and it was smoking enough on deceleration that folks preferred not to ride behind me. The seats were still fine, with close to 100k miles on them.