Carb overflowing despite changing float valve

[Mark]

Hi all,

My 3AJ Tenere has an annoying habit of leaking petrol from the carb overflow hole in it's float chamber.

As far as I can tell it only happens when I turn the engine off, I have often looked when I have had to wait at junctions and never seen any sign of a leak.
Also, no amount of tapping the float chamber will stop it. I have inline fuel filters fitted and have changed the float valve and it's O-ring.

I guess float must be sticking on it's pivot pin but they seemed OK when I had the carb apart, and I am puzzled that I have never seen it happen when the bike is ticking over at junctions.

Are there any other possible explanations?
Could a faulty fuel pump somehow generate too much pressure so then it overcomes the float valve when the engine is turned off ?
Should the in-line fuel filters be able to empty when the engine is not running, and hence the fuel pump not operating?

Thanks for your thoughts

Mark