lvelhead, was it, who listed on his website, all the year-by-year differences? I think someone else (an attorney) ended-up with the web address, and now if you try to find the VMax content, you get solicitations for a personal-injury attorney. I bet Sean Morley knows where the list is, of yearly changes. I think the VBoost manifold was maybe smaller I.D. for '85. The VBoost was increased in size when the bike didn't meet EPA reg's at the time, and they made changes to the exhaust. The larger VBoost was to compensate for the exhaust changes. That's what I recall.
Nothing to do with the carbs, unless you bought yours in Denver, so they had leaner jetting, probably a dealer-installed process.
Anyone know different, please feel-free to contribute. USA referenced, as many foreign market bikes had limiters to the movement of the CV slides to meet HP restrictions, or they did-away with VBoost altogether.