Vacuum Secondaries

RogerRamRod said

I always thought if you felt them open, it was either because the primaries already ran out and the sec. were opening late. Or if you felt a bog, then a sudden rush that they were opening too soon, because you were waiting for the engine to catch up to the air and fuel the sec. was adding. Either way you really shouldn’t feel a transition.
But yes, the quick change kit and spring assortment was invaluable.

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The bog is always because they opened too fast. The VS carbs only have the primary side accelerator pump. Once that pump has exhausted it's volume, only the airflow will create fuel flow through the secondaries. The bog is the lean spot that will happen until the airspeed is high enough through the secondaries to draw fuel out the boosters. I've seen many attempts to fix that - including adding the 50cc accelerator pump to the primary side, smaller shooters, etc. But the real fix is slowing the secondaries down.
Funniest part is the VS carbs are easier to set up than the DP. Most engines are simply passing way too much fuel with them, but the owners don't understand enough about how the carb and ignition work to really properly tune. That's why the plug-and-play EFI is such a huge market now and will only get bigger.