[SuperHart]

Even though this subject has been discussed before here are a few ideas. Bog is usually caused by the throttle plates opening too quickly without a sufficient fuel shot causing a momentary super lean condition. When air flow through the secondary venturiis picks up enough to siphon fuel the condition disappears. This is why nearly all auto manufacturers go with vacuum secondary carbs rather than mechanical ones. With vacuum secondaries, the secondary throttle plates open gradually as engine demand increases. If you get a bog with a vacuum secondary carb when you nail the throttle Holley suggests installing a stiffer spring in the vacuum pot. That goes for dual quads also. With dual quads you must have a hose connection between the two vacuum pots to balance them.

Nearly all dual quad intake manifolds have runners connected to equalize and balance the vacuum and mixture signal to all cylinders. If the dual quads are reversed like on the Ford FE motors, the primary throttle bores of the primary carb are near the center of the motor and do give an adequately balanced mixture to all cylinders. Therefore, you can set up your linkage in a progressive manner so the secondary carb opens later than the primary one. Here again, crisper throttle response without the bog.

When setting the idle mix on a dual quad setup remember the rule of thumb for setting one carb, the idle mix screws turned out 1 1/2 turns from lightly seated. Now that you have TWO carbs, the settings are usually around 1/2 that for a single carb, i.e., turn the mix screws out 3/4 turn from seated on all four idle screws. The idle speed screws are also set the same way and are usually 1/2 the number of turns out. It does take some fiddling to get things right but the end result is worth the effort.