Thanks for all the replies, I think the first plan of action will be as you say Tim, see if the pipe is clear. We will drop the tank as well as the sender nit does work I think but when filled we shw empty and vice versa!
Chamba, a guy helping us with the carb mentioned about a venting pipe, does it run out of the tank, or a through the fuel cap type thing. He mentioned that in theory it stops the tank causing to much of a vacuum and sucking its own tank through the engine. I was not really paying too much attention, I was too busy giving evils too Fontaine.
But it explains why we struggled getting home from the Commer meet anyhow. And I self diagnosed which is another thumbs up to our own personal 'Mr Miyagi' - Tim!
Jon&Cara-Gramarye Fontaine