Motoscrubs.com

All of these are fabulous suggestions and a couple in there I overlooked. But back to the original observation that has me puzzled: things were fine and then they weren't. In insufficient needle valve would have been a problem from the beginning. It didn't progressively get smaller in size.

But you did bring up a couple items that have me wondering. Specifically, the float bowl drain hose. Need to take a look at that.

A long shot but possible,
You have a fibreglass fuel tank?
Old glass tanks start to dissolve with unleaded fuel.
Sticky residue from the resin coats the jets and needle and reduces the fuel flow.
This has happened to me many years ago with a Pantah and a NCR type tank.
Strip the carbs and clean and it was good for a very short time then do it again.
But I assume your tank is modern and able to cope with unleaded fuel?

Graeme

Yeah, tank fully sealed. All is well on that front.

Occam's razor. It was a clogged carb.