I assume this bike never could get started and nothing you did recently could have caused this change in behavior? Or perhaps it has been getting worse over the course of time..
Sometimes spraying with carb cleaner isn't enough.. there are tiny hidden passages and it takes strong compressed air and soaking in solvent to blow them out.
Remove the idle speed screw. (it's the one with a spring behind it and it's tip makes contact with the throttle linkage at the carb).
Below / under that idle speed screw is another screw. You can see it's head but cannot remove it until the idle speed screw is out of the way. Remove this other screw and look inside the hole.. There is a really tiny jet pressed into the bottom of that hole.
That jet delivers air to the "emulsion tube" (the brass tube stuck up above the main jet). This jet and passage pre-mixes air with the fuel as fuel comes up the main jet and into the tube.
The emulsion tube is another often neglected thing that a thorough cleaning should include. It should be removed and cleaned. It's just lightly pressed into the cavity above the main jet. Push the tip of it down with a pencil to get it started on it's way out (You can see it's tip sticking up into the venturi). Air pressure can blow it all the way out or pound the carb into a folded towel or another protective padding until it drops out.
If you're positive the carb is truely clean, then look for loose nuts and bolts especially around the carb intake manifold. Loose head bolts are another thing although they dont seem to loosen by themselves on this particular engine..
Since it fires up with starter fluid, it does seem to be a fuel delivery problem. The only other likely thing would be extremely low compression.