Well you were pretty much spot on.
The problem is in the fuel line from the tank. One is ok the other not so good. I put it on Prime thinking it would feed from both lines but it turns out that prime works off one line and not the other. And that line was the duff one

I took it out for a thrash and it does not starve now, it runs ruff but that might be the choke as I cannot seem to find rubber insert that does not swell. I put a Nitrile oring in as thats petrol safe but it might be too small so choke fuel is leaking by.