This “project” bike has over 63,000 miles on it. It’s not uncommon for the timing chain and crankshaft sprocket to wear enough at that mileage to affect valve timing. Too much slack causes uneven timing of the valves. If valve timing varies, then ignition timing will not be optimal. In situations with a lot of wear, the chain can be heard slapping inside the motor. As I’ve never heard this bike run, I do not know if the timing chain is that loose, but that much slop in the timing chain is more common at 100,000+ miles on the chain.
I repainted the inner timing cover and you can read about that work here:
Here is a link to the document showing how I do this work and some videos summarizing the work.
VIDEO: 1983 BMW R80ST Remove Timing Chain, Crankshaft Sprocket & Nose Bearing
VIDEO: 1983 BMW R80ST Install Crankshaft Sprocket And Nose Bearing
VIDEO: 1983 BMW R80ST Install Timing Chain
VIDEO: 1983 BMW R80ST Install Inner Timing Cover