Well, this will probably get me in trouble but.... Everyone seems to think that the spring holds the throttle plate centered and it does not. That spring works in torsion to close the throttle; not in compression to hold the shaft. If it were in compression to hold against the shaft, it would push the shaft and plate over against the other side of the carb; not center it. Some carbs have a "C" clip on the opposite side that helps locate the butterfly plate and shaft, some don't. But in any case that spring doesn't do it. Now I will go along with the argument that leaving the spring on may damp some vibrations and help prevent carb throat wear, but that spring is there to close the throttle, not tension/push sideways against the throttle.
Oh boy, I can imagine the comments on this one....
AV8TOR