I once had a carb that had a sticky needle. The needle would stick shut and could not open to allow fuel to enter. (The needle that is moved by the rubber regulator diaphragm.) You might look at that. I imagine you have already checked for any air leak at the carb to manifold gasket. Does the fuel tube fit tightly onto the fuel inlet on the carb? The tiniest air leak in the fuel line to carb setup will prevent them from wanting to draw fuel. I have had connections that I would have sworn were good, but leaked a bit of air and caused fuel draw problems.

I usually use WD-40 to verify flow through each passage. Take out the mixture screws and disassemble the carb. Find the orifice(s) that feed fuel from the regulator side of the carb. Blow through those and you should see WD-40 bubble out of the mixture screw holes. Then blow straight into the mixture screw holes with the WD-40 while looking into the carb. When done through the high speed hole, you should see fluid come out through the high speed jet, and when done through the low speed hole you should see it squirt out through the two or three idle/midrange holes in the venturi. Do the same for the fuel entry holes in the fuel pump, etc. Also, literally verify that the little screen can flow. They can plug up with a coating of nearly invisible crap and look ok but not flow.

Anyway, at least fire it up with the DLE 20 carb and see how it runs....

AV8TOR