You got the winner so far Jim!
On the later XS650 petcocks with the combo screen reserve pipe.
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That whole assembly can loosen and flop off if it isn't tight in the petcock, so if you are all happy thinking: man I'm getting really good mileage, past 150 and haven't even hit reserve yet. You might be surprised when you switch to (NO) reserve.
Hint if they don't seat tight I cut some shims from pop can and tighten up the fit.
Now you tell me. Where were you 15 years ago when I was pushing my '83 for that very reason?
I solved that problem. I did away with the in-tank filters and silver-soldered a short piece of stainless steel tubing in the reserve side of the petcock. Then went to replaceable in-line filters in glass tubes.