Well, this was a first! This afternoon, the R80 started cutting out...just slightly at first and then going completely dead. I coasted to a stop, checked the battery connections and checked the carbs for fuel.
All seemed to be good. After a minute, the motor fired...and I got about a block, and it died again. More checking and it fired up again and I was able to make it home.
Additional facts: fresh gas, with about a gallon down from a full tank. Mileage: ? unknown to me. Speedo was replaced by previous owner, but bike does not show extensive wear. I had a tankbag on it for the first time, and the possibility of low air pressure in the tank did occur to me. This happened on my 78 R100. Today I noticed a "whoosh" when I pulled the hose off the petcock to remove the tank at home.
Still, I'm learning toward an ignition problem. Tom Cutter said not to pull the plugs to check for spark with these mono-shock models, so what's my next step?