Mixture cable
Is the mixture cable attached and going full throw both ways? If so, try pulling the filter screen which is under the fuel inlet of the Ellison. Ensure good fuel flow with the line disconnected. Look up the throat and ensure the mixture tube rotates when the mixture control is moved. Holes point down at cutoff and are 90 degrees at full rich. In that same vein, ensure the mixture lever on the Ellison has not come loose. It should be safetied, but you never know. That could cause the mixture tube not to rotate.
If it's an older EFS 4-5 (O-360) or any EFS-4 there should be a small tube running from the bottom of the bell inlet to the regulator. I believe the newer EFS 4-5 have this incorporated internally so wouldn't apply.
Just a few thoughts.