I know this is a bit late, haha, but I'm fairly new to the forum.
This is my take on quietness of a Lister/oid engine.
Everyone knows a petrol/gasoline engine is quieter than a diesel engine.
Everyone knows that a single cylinder engine is noisier than a multi cylinder engine.
Everyone knows that the bigger the cylinder capacity the more noise you get.
So a large capacity, (1450 cc), diesel engine with a single cylinder, isn't the quietest beast on the block.
Saying that.... These engines, original or clone, still do what they were meant to do, convert diesel into power and they do it surprisingly well.
Even with a pepperpot muffler, these engines are quieter than the average Harley Davidson wth compariive capacity, gasoline powered and twin mufflers.
So, I suppose I m going on the awkward side of the request, to make a lister/ oid quieter...why change what has obviously worked for over 100 years? These machines were built for farm and factory, not a terraced house in suburbia.
If quietness is required there are many natural gas powered multi cylinder generators available that are very quiet.
Changing what simply works, I'm sorry, is nonsense,