Mmmm……are the needles just a fraction too big/tight ? Nothing a very light rub with 1200 grit wet/dry wouldnt sort.
Does seem to be a mystery, but it can ONLY be floats/needles issue. I am not sure about catch tank , seems a lot of work , but of course it solves the issue temporarily. As a question , and i have not tried this, how about a half open fuel tap ? Does it even do this ? Maybe partially block the vent hose on the fuel cap or stick a tap on it.
I hope it clears up for you, not sure what else to suggest.