Make sure the two model years use the same length intake boot, or if not, that you can still wiggle the carbs into their airbox connectors. My '75 550s both have '77 carbs, and the connectors between the carb and the head are different for the different years. Live and learn. Once i got that squared away and learned the correct float height adjustment for '77 carbs, there were no problems. That's what I get for assembling two CB550s from a pile of mixed-year parts.
