I have the best overall results with the Teapot secondaries being activated with a vacuum signal rather than with some form of mechanical linkage. Mechanical secondaries if activated with the rpms being too low will provide inadequate air flow through the carbs for them to provide any performance benefits. Coughing and/or backfiring through the carbs is a common symptom of what happens when the secondaries are converted to mechanical activation without the secondary side fuel system being made much richer in which to compensate.
The model 4000 Holleys (Teapots) use the same vacuum secondary springs as the model 4150/4160 Holleys which makes tuning the secondaries much easier on the dual quad setups. Using either the long yellow or short yellow springs from the Holley spring kits are a good starting point for the dual quad Teapots. An equalizer tube or connecting line between the secondary pots will also allow both carbs to open more equally. When the seconardaries are opening correctly, it will be a smooth transition without any noticeable jerks or bogs taking place.