Are you saying that the float bowl fills with fuel?
If it does but there's no sign of fuel getting into the engine, the main jet or something in that area is clogged or not working.. Like it might be the main jet is clogged or maybe the jet needle (if there is one) is detached or stuck and does not move up when you twist the throttle.
If the bowl is not filling with fuel, the float itself could be stuck and can't drop down, allowing the float needle to drop. Perhaps the float is rubbing on the wall of the float bowl when assembled or hitting something else.
Or there could be blockage in the float needle passage.. Or the float needle could be jammed, stuck up in the float needle orifice.
Or a fuel filter/screen near the fuel line entrance in the carb could be clogged..
Or the carb could be assembled wrong. For instance sometimes a float bowl can go on in two ways, only one of which is correct. If it's wrong the float may not be able to move.
Trace the fuel path from the end of the tank hose all the through the carb to the venturi.. Fuel is being blocked somewhere and you gotta find out where.