So is it the pump or the carb? I never had any luck with Holley carbs. My first runner, I had a 650 installed. Engine ran really rich, replaced it with a 750 dbl pumper. It still ran rich, my father in-law and re-jetted, swapped power valves trying to lean it out. Always had the same issue, no matter the setting, the carbs ran rich. My father in-law ran 850 on his 440 dart race/bracket car and had no issues with Holleys. We were bot confused and could never figure it out. Installed a 750 Ederbrock on the engine, problem solved. It was as if the Edlebrock was made for the engine. Good luck with your swap.