All great now - a bit of a rush last night to pop the carb back on and test so I whipped it off to double check and cleaned it again, running beautifully now.
The primer system being stuck down was the issue I'm sure as testing again and holding primer plunger down re-creates the symptons.
I think the reason it did this after running fine on the sea previously was that when flushing and running dry at the last moment to clear as much fuel from the carb I pull the choke out until it finally dies, this being held in together with a few years of varnish/crud must have meant it chose that moment to stick down, hence the issues the other day and three weeks later
I've got the mixture screw where it seems happiest running between too rich and too lean (about 1 1/4 turns out) and killed/re-started a dozen times - running very nice now so fingers crossed for the next trip.
Thanks again to all for the input.