If you:
-got fuel coming in the tube
-and you got it to fire when you put fuel in the carb directly
Then you must have a blockage in the carb nipple-banjo-thing (where the fuel tube attaches to the carburator) or high speed needle assembly.
That happens when an engine is sitting for a long time with fuel in the carb nipple there.
So that is preventing the fuel from flowing into the carb.