holley carbs

Generically speaking, carbs can be lumped into 2 different categories...vacuum secondary or double pumper. Vacuum secondary carbs are when the secondary throttles are operating by a vacuum signal. They can be identified by a vacuum pod on the carburator. Double pumper carbs are when both primary and secondary throttles are mechanical driven. There are no vacuum pods on these carbs and can also be identified by accelerator pumps on both he primary and secondary side of the carb. There's more to it but that's it in a nutshell.