I thought a new thread would be a good idea for looking to source new Bowden cable/conduit tubing for the O&R throttle cables.
I have a long NOS conduit here (the inner wire is a separate part) which I've measured today, with the plastic sleeving on it measures approx 0.145" to 0.15" (depending where you measure) and the steel core measures 0.125". The separate inner wire measures approx 0.047", this may vary slightly too. I noticed the plastic coating is removed where it enters the carb on my mini-bike.
Here is a thread on another forum (which was one of the first search results I found the other night), there are a few different suppliers mentioned that have different types of Bowden cable.
https://forums.stanwinstonschool.com/discussion/4182/extra-fine-bowden-cable
One of the links has some conduit tubing that might be suitable, the second one in the list could be suitable with the plastic removed (OD is 0.153" with plastic coating), maybe email them to confirm.
https://bergencable.com/_media/products/control_cables/pdfs/conduit.pdf
David