Mine did something like that - I finally pulled the float needle valve and stuck a tooth pick up there and a flake of junk came out of where the gas feeds in.
Apparently the seat of the float value was holding gas in there and it dried up and make it’s own little flapper that was closing half the time... drove me nuts for a couple of weeks as I tore things apart multiple times... then I finally put that pick up there and saw it fall out... then it ran like normal.
