Oak Okleshon blames Bing slide valve carburetors for pre-ignition. The carbs produce a lean fuel:air mixture during acceleration. These carbs have a built-in accelerator pumps. Perhaps the pumping function is degraded?
Robert "Snowbum" Fleischer is located near Lake Tahoe and I'm certain he can recommend someone who can dual-plug your R60 if you elect to go that route.
The Bing constant vacuum carb is less vulnerable to this condition. Oak recently provided a lot of information about the R60/5 pre-ignition in Airtech. Did you read it?

Those Type 53 mechanical Bing carburetors are known to be troublesome. I have never owned for myself, or advised any owner who could make them perform properly after they had gone bad/ neglected/sallow/well aged/etc. That accelerator pump, which is built in to the main jet assembly, is a brilliant piece of engineering conceptually, but is troublesome in real word use. I would ask how can a main jet assembly deliver a consistent air/ fuel mixture when it is supposed to serve the dual purpose of doubling as an accelerator pump? I have taken these Type 53 carbs apart, and when you understand what is going on inside one of them, you will question how they ever worked at all. The Mikuni conversion is superior.

The R60s (and R50s) are known for carbon buildup in the combustion chamber. Get a pair of head gaskets and go to work. The British refer to this as "decoking" . I use a small gasket scraper, a table knife and some sand paper to clean up the piston crown and the chamber of the head. Makes a REAL difference!

Matt Parkhouse

Thanks Matt,
This was my idea from the get go as well. Good to hear that other people have done it. When you look down the spark plug holes with a flashlight you can see a ton of carbon build up. In the long term I think I'm going to swap a 75/5 engine and drive-train to get that extra horse power on long trips and hills, but for now I will "decoke", replace accelerator pumps, and replace advance springs. Hopefully that at least makes it rideable one-up.

I LIKE the slide Bings on the R60s...... When clean and nicely set up, they give a good ride. Stone-age simple too. My wife and I rode all over Europe and N. Africa on a pair of R60/5s that I set up. In 9,300 miles, no knocking or pinging noted. They DO run rich on occasion and thusly, can cause carbon buildup. Wish I had those right now....

Matt Parkhouse