No modifications, just pics of things to check. That one carb with the red marker stripe is the path of your air correction passageway to the main jet holder hole. These carbs have a 1mm or #61 twist bit equivalent, brass air correction jet pressed in the casting. Not sure what You are cleaning when you said you've had them off multiple times? But make sure that correction jet and passage is completely clear! A plugged correction jet will make it run rich and erratic. And, like Mikaw suggested, record the Main and Pilot jet sizes and brand type. These carbs, if true 72-73's used a unique taller #20 pilot and 112.5 Main jet originally. Couldn't count how many times i've ran across persons installing some main jets like 135-155 in them. Total misconception of thought, I got me a header, gotta be high performance, so i'll jam the biggest friggin jet i can find in there.