1976 Buick Century will not idle when engine is warm.

My car will idle and run fine as long as the choke is engaged. when the engine warms up it will not idle. As soon as the accelerator is let off the engine dies. The car runs fine as long as you are accelerating. All the hoses are good, I have added new gas, and used a whole can of carburator cleaner to loosen the varnish. The mechanic said it would require a new or rebuilt carburator which for this car is difficult to find. He checked the EGR valve and found it is functioning properly.