Ok, it's all shafts and no cables. There is a sprung stop screw on the throttle body just behind the air filter which seems to determine idle. Have turned in one turn and today it idled for about two minutes before dying. Fired up again immediately. But at increased idle the gears crunch a bit. It will idle away in gear forever. But in neutral just seems to miss after a bit and cut out. Idle mixture maybe? Where is that? Or something else.
Carb has been off, cleaned, float level sorted, full service, new plugs and control cables. Just the godforsaken idle out of gear is a pain.