First thing to check is to see if the choke is closed completely, as mentioned. Also, as Dartnut alluded to, if compression is low, the engine won't have the "suction" to pull gas out of the bowl into the venturi's. Those choke flaps had several holes in them. I worked on one with low compression and bandaided it by making a new choke flap w/o the holes. I told the customer the engine was shot (I did a leak down.), but it would work for a while.
Carbs don't need to be rebuilt unless gas has gone bad and clogged it up. Partial clogging leads to rpm "hunting". Bad gas carb problems can range from needing a simple flush, to a rebuild, to replacement.
