yes.

a 107 will help but the looks of things you need to sort out float heights 19mm from the face of the gasket to the pimple in the middle of the float

then its a case of looking at the pump and lines just in case all is not well there.

Thanks Sean, the fuel level was ok, I think I took the picture when I was half way through sponging the fuel out of the bowls before cleaning them. Can't get anything past you!

Could the heat on the day have exacerbated the problem with the fuel / air mix (due to the ingredients of modern petrol), or am I barking up the wrong tree, and it probably was just a bit of 103 sized grit getting in the way?

Fuel pipes are pretty new, including the one on top of the tank, and a new pump was fitted some time in the last year.

Is a 107 primary just considered 'best practice' these days with modern petrol mixed differently to the olden days?