Actually a 1000 CFM carb will have very large jets so I would think that even though the engine is only calling for 600 CFM it would still be running rich. While we know most of the details on his motor we still don’t know what part number carb that he is using.
I was talking about airflow not fuel flow. You can put a thousand CFM carburetor on that motor and properly jet it and it will use as much air as it needs. It's up to you to jet the thing.