Two things come to mind.
Dougand got the first .
The other, particularly as this is an old old machine, crank case seals.
We know it stars fine if you put fuel into the cylinder, lets see what happens when you put some starter fluid in the crankcase by spraying through the carb throat.
If it doesn't fire right up that would suggest that the seals are shot & you are sucking air in past the crankcase seals and not through the carb.
It won't hurt to test the carb either,
Slide it off the engine, turn it sideways and blow air through the carb throat.
You should get a nice flow of atomised fuel out the other end.
If not then there is a blockage in the carb.
Well that makes 3 looks like my counting is a bit sus.