The big secondary throttle plates on the QJ are actually mechanically opened, but there are two "fail safe" modes incorporated into the design. When the choke is applied, even a little bit, the secondaries are blocked shut with a mechanical lockout. Once the engine is up to normal temp and the choke is released, a spring loaded air valve prevents too much flow through the secondaries. The Pontiac 230 cubic inch overhead cam engine actually came equipped with a QJ carb! Some of the Rochester 4G square base 4 barrel carbs back in the 1950s also used spring loaded secondary air valves.
Jerry
