How significant difference does it make if you suck air against centrifugal force, Brett? Is it a noticeable difference really? I've never thought about it.
My engine sucks fuel about 0,25ml/second, that much replacement air is needed every second. L
It is easily possible that the fuel can run out one side of the tube, while air runs in the other side. You can probably get around it by putting in a smaller diameter tube (so surface tension prevents it from separating), but, then, you can't get fuel in it. And before anyone jumps on "well, that never happens to me", right, it never happened to some people, it has happened in rare cases. So, again, why create a potential problem, that might or might not crop up, when it is trivial to do it correctly?
If nothing else, you can stream out fuel (pressure = 2.5gs x the density of the fuel x the distance from the fuel surface) while the engine keeps running and taking out infinitesimal through the spraybar, and blurp a bit of air to keep it running, then stream out more fuel. And yes, I have seen that happen, it is not impossible. Of course while it is streaming fuel out, it's also leaning out, making your 2.5gs go to 3 gs and making it stream faster.
There are a million little things like this, none of them all that big by themselves, but the entire point of asking people with more experience it to take advantage of is to move beyond a small bubble of "I tried it once and nothing bad happened".
Frank asked a question, it was not a silly question, I gave my answer, I think I explained it as well as I can. As always, it is just advice, no one is compelled to follow it, and the chances that you will have a problem (with this by itself) is not high.
Brett