Join Date: Jan 2018
Location: North Dallas area and UP of MI, average snowfall 202"
Not sure if you were watching flow with the line disconnected, or the bowl off, but if the latter, note that the needle valve opening is probably closer to 3/32" tham 1/4, which will be the biggest limit in flow. If the former, perhaps the line is breaking down and closing up internally - changing the line is quick, cheap, and easy on most machines . . . Might also check flow with the line off the tank in case any internal filter may have gunk in it.
On another note, I've also had this happen with crap in the bowl plugging the mets when running, but falling clear when not running, but un;ess the crap is still in the line, the replacement carb pretty much ruled that out.