Re: Higher flow petcock?
Is it the petcock that's faulty or the little screen that screws onto the inside half of the petcock?
That little screen gets clogged up easily and will slow the flow down to a trickle. If you're using an in line fuel filter this screen isn't needed.
The other part of this issue is the tanks the self need to be cleaned out really well before putting fuel in them since the Chinese like to send us gifts of metal shavings, paint chips, shredded newspaper bits, dirt, sand, and who knows what all else inside these tanks. This stuff alone can clog that little plastic screen filter shortly after fuel is introduced, or it can clog a small in line filter, and if you go filter less you'll find this stuff in the carb's float bowl and possibly blocking off the needle and seat valve or the main jet.
The stock petcock will flow plenty good enough if there's no other junk in the tank, but if the tank wasn't cleaned out Good before putting gas in it, it's pretty much guaranteed that little plastic screen filter is stopped up preventing the flow.
With the tank cleaned and that plastic screen removed (we all use in line filters, right?) it'll flow plenty good enough.