So, following a query from a visitor to the Thumper stand at Stafford, I thought I'd repeat this tip, which was originally posted by Blew. Where the choke cable goes into the carb, it has a plastic threaded nut going into the alloy carb. The plastic thread inevitably fails, so you need a replacement. From Honda, you used to be able to replace the whole thing, but at £40, no longer available. But for £7, on eBay, 301973817019, you get a scooter choke which is identical. Just cut through brass plunger, and you are left with plastic nut and spring. Or, do what my talented, violin making mate Peter did, and turn one out of brass