These tanks are notorious for having all kinds of junk inside them from the factories in China like metal shavings, paint chips, small pieces of news paper and who knows what all else. If you didn't clean out the tank before installing the petcock and that little screen filter then this is probably why it just barely trickles out.
I've had a customer's bike come to me with a similar problem where it would cut out and then work and then cut out again and it had the same problem, the fuel would just barely trickle out of the tank one time than it would come out as a steady stream.
I took of the petcock and poured the fuel mix into a waste oil container then washed out the inside of the tank, the little screen filter on the petcock was covered with junk from the tank so I took it off and blew it out with compressed air, then made sure nothing was obstructing the petcock, put it all back together and refilled the tank with fresh mix, opened the petcock and let it drain back into the gas can and problem solved. This one also got a new fuel filter just to be safe, but it was flowing way better just by cleaning all the junk out of the tank.
If you were running without a fuel filter then definitely check the carb too, things can block off the needle and seat valve and main jet which will cause the engine to cut out intermittantly and randomly... This problem can also be caused by the fuel valve on the NT Speed carb, I've had one that would cut out like this and found little rubber particles blocking off the needle and seat valve and found the culprit to be that rubber disc that's in the fuel shutoff valve that's built onto the carb so I just gutted it out since there's really no need to have 2 fuel valves anyway.