An update on my GMS 76, complete with knock & erratic tuning. The knock at idle is still there but seems to be subsiding (don't ask me why) & drilling the fuel inlet hole in the NV assembly has actually cured the erratic tuning -- now it holds a steady 11,000 RPM with an APC 12-8, without sagging or flame-out. I'll let you know if the knock is ultimately terminal, or just an annoyance.