Not sure if I understand exactly what you are saying. Do you mean you keep going faster on the primaries then just before the secondaries start to open it goes lean 16.5? 3,500 rpm at cruise@ nearly 100mph?
Then I would suspect high speed cruise vacuum is very high and the power valve is late. If this is a correct description then that isn't really a big problem unless you plan on doing a lot of 90mph roll street racing.
Yes on the center carb, if I open it up to where the linkage is just about to open the end carbs it goes lean, yes it's not a big concern. Mostly concerned about the rich low speed cruise and the tip in on cruise.
