Leaking front carb - SUs

[Paul2500S]

Help! I’ve got petrol coming out of Front carb air intake. This happens a couple minutes after turning engine off and continues for an around a hour.

I’ve changed floats with rear carb (which doesn’t leak). I’ve tried two different needle valves as well as swopping with rear carb. I’ve also put a paper gasket on the thread of the needle valve in case it comes through the joint.

I’ve reduced the fuel pressure down to just over 2psi via pressure valve.

The front chamber fuel level is about 1/2” lower than the rear one.

Before I go and order some more needle valves is there anything I’m missing? Any ideas on what could be the cause?