Can't seem to stop fuel draining from carb float bowl overflows (at bottom rear of float bowls).

I've set-up float heights now, perhaps, 8 or 9-times (13mm - using the methods described numerous times on this forum). Happy that heights are as right as they can be (I think!).

I've cleaned the brass float valve (rubber faced) plunger seats (several times).

Replaced plungers for new items.

BUT - Still overflows (with fuel tap open and engine off. But, with engine running, it seems demand for fuel from motor exceeds supply from tank and fuel doesn't overflow from carbs).

Seems can only be either / both fuel level too high / plunger no sealing in seats. But, seeing as I've done what needs to be done with respect to those potential problems and STILL fuel overflows, I'm now a bit stuck!

Any other ideas? (other than never having fuel tap open and engine off! - don't trust myself to always remember to do this!)