Forgot to add, T2Racing now do replacement float valve seats too. Probably stating the obvious, but if the float height is correctly set, the only reason you will be seeing overflow is if the valve isn't fully seating/sealing.

https://t2-r.ocnk.net/product/370

It sounds like a similar situation you can find with spark plugs... they may appear to work perfectly well when tested outside of their normal working environment, but once fitted exhibit faults.
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Andy.
NSR-WORLD.COM

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