Sprint SU Float Leak

[Malsprint]

I changed the needle valve on the rear float bowl because it was leaking quite a lot. The front one seemed to be fine but I also changed it at the same time. The needle valves are the newer design with a spring loaded pin. Now the front one has developed a small leak. I changed back to the old needle valve but the leak remains.
The fuel pump is delivering a max of 3psi and I have fitted an inline fuel filter after the pump. The float bowls and needle valve are clean with no sign of crud or debris. I also cleaned the metal fuel tube between the rear and front float bowl in case there was any corrosion on the inside but that also seems nice and clean.
I applied 3 psi of compressed air to the float assembly off the car and it seems to seal fine with very little pressure from the float on to the valve, just barely touching.
I fitted a catch can to the overflow to measure how much was leaking and it is a very small amount less than a teaspoon on a 30 mins run. It only appears to leak when I take it for a drive. I am wondering if rather than a leaky needle valve, could it be fuel splashing out of the overflow during braking and perhaps this is normal.
The overflow on the rear faces toward the back of the car which may explain why I don’t see the same type of leak on the rear float bowl.
Any advice.

[MIG Wielder]

On my 1850 I went through a spate of new needle valves until I looked at the top of the plastic floats. On both floats there was a noticeable dimple where the metal plunger operates. I think the plunger was sitting in this wear depression intermittently.
I tried filing it smooth but this increased the float heigt. More flooding !
So I changed both floats and it's been O.K. since.
And yes, SWK is very high mileage.
HTH,
Tony.

[GT6Don]

Burlen are selling HS6 floats that are height adjustable, comes with a leaflet advising what the float height should be as well - 3mm I think. Not cheap though.