@RS-60 mark posted:
Be sure to back-flush the fuel inlet port and jet with compressed air or carb spray before installing the new valve. Any fleck of dirt or rubber bits ('ethanol induced') that can wedge between the needle and seat will continue the same problem you are having. The fuel inlet circuit above the valve must be clean. When you blow it out, do it over a white rag to see if anything comes out. If you find black rubber bits, then you'll need to look upstream and replace whatever is deteriorating.
Don't use any more than about 10-15 psi if you use compressed air. A little carb spray should be sufficient.
I've found that Solex/Kadrons will run for YEARS without clogging up. They are trouble-free compared to Webers or Dells. The idle jets are certainly not any bigger or smaller, the design of the carbs just doesn't promote troubles. Musbjim knows...
On my recent engine build I noticed something interesting. You know those big washers with a thin black rubber washer that go on top of the CB air cleaner tops? When new, little tiny pieces of rubber come off and fall through the stud holes RIGHT ON TOP of the carb every time they are removed or installed. Where do you think they end up? Right in the idle circuit air intake. After a while, the rubber gets worn enough that rubber stops chunking off.