AFB starves on the secondary side

I know this thread is a few months old. But, it’s often over looked and hasn’t been mentioned in reference to a full throttle/secondary bog/hesitation. If your kickdown is not operating properly at the correct speeds. You will have these symptoms of a bog/hesitation in the secondaries. Because the carburetor needs the higher rpms from 2nd gear when the tranny kicks down near full throttle. In 2nd gear or 2nd gear rpms the fuel pump is pumping more gas that the carburetor needs to sustain or build more power near full throttle. When the tranny is in Drive at a much lower rpm and you hit the gas near full throttle at that lower rpm it leans out the mixture. Because the valve fully opens suddenly and introduces a rush of sudden air. There isn’t enough gas to follow.

The bog or hesitation goes away as you let off the throttle because you are slightly closing the throttle valve allowing the fuel pump to catch up, pumping more gas and reducing air. Drop the tranny down into 2nd gear manually at 35-45 mph. Mash on it and hold it there for a good distance. See if the problem goes away. I bet it does. Your rpms are too low for that throttle response. The only way you can over come that is raising the rpms. That is part of the kickdown function. You can’t correct that problem doing anything to the carburetor. Jetting, etc won’t fix it. The rpms need to increase. If the throttle is increased sudden enough. That’s the transmission’s job if it’s working as intended. This is one of a few reasons why it’s so important that the kick down works properly at the correct speeds. Not only for the transmission‘s health. But, the engine needs it to work properly under certain circumstances. It affects how well the engine actually runs on a street car. It affects the carburetor getting the correct amount of fuel under certain throttle load circumstances. 3/4 to full throttle. Low or high rpms. With a manual transmission your increasing the rpms, amount of fuel pumped manually. A manual transmission doesn’t have this problem. If a manual transmission bogs in the highest gear at 3/4 to full throttle. You down shift manually. This over comes a bog hesitation because you are increasing rpms and fuel as a result. Assuming your pump is efficient enough.