This has been going on for a few weeks now, I've pulled the carbs apart couldn't find any problems, diaphragms good, there was a slightly looking dodgy plug on one of the vacuum ports which I ordered a replacement for. Couldn't find any other leaks, checked the coils all normal 5.8 ohms across the terminals and 29k to the plug and terminal, in spec. Pulled the gas cap apart. Nada. Wondering if this could be caused by a valve not sealing, possible but just didn't feel right.
Got delivery of the replacement plug and wa la. It's golden again, so I thought I'd put this thread up because it's hard to spot. Below is a photo of the plug (cap), which is part no. 40 on the diagram. It's pretty thick rubber and I could not see any leaks but it did have some cracks and it was a bit swollen. I covered it with silicone sealer while I was waiting for the part but that made no difference. I put the new plug on not really expecting anything to change but it fixed it instantly believe it or not but this dodgy plug was causing all the strife.
I moved the clip position on the needle down one while I was in there so it's running better than ever now!
(https://s9.postimg.org/yw5wq3k8b/carb.jpg) (https://postimg.org/image/yw5wq3k8b/)
(https://s9.postimg.org/br03hwhcr/plug.jpg) (https://postimg.org/image/br03hwhcr/)
Amazing--congratulations. Who would have thought such a fix?
Good info, thanks for posting this. Hopefully it helps someone in the future. :cheers:
'Solved' threads are the best! Applause!